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1.
Evolution of Duplicated <Emphasis Type="BoldItalic">reggie</Emphasis> Genes in Zebrafish and Goldfish 总被引:1,自引:0,他引:1
Málaga-Trillo E Laessing U Lang DM Meyer A Stuermer CA 《Journal of molecular evolution》2002,54(2):235-245
Invertebrates, tetrapod vertebrates, and fish might be expected to differ in their number of gene copies, possibly due the
occurrence of genome duplication events during animal evolution. Reggie (flotillin) genes code for membrane-associated proteins involved in growth signaling in developing and regenerating axons. Until now,
there appeared to be only two reggie genes in fruitflies, mammals, and fish. The aim of this research was to search for additional copies of reggie genes in fishes, since a genome duplication might have increased the gene copy number in this group. We report the presence
of up to four distinct reggie genes (two reggie-1 and two reggie-2 genes) in the genomes of zebrafish and goldfish. Phylogenetic analyses show that the zebrafish and goldfish sequence pairs
are orthologous, and that the additional copies could have arisen through a genome duplication in a common ancestor of bony
fish. The presence of novel reggie mRNAs in fish embryos indicates that the newly discovered gene copies are transcribed and possibly expressed in the developing
and regenerating nervous system. The intron/exon boundaries of the new fish genes characterized here correspond with those
of human genes, both in location and phase. An evolutionary scenario for the evolution of reggie intron-exon structure, where loss of introns appears to be a distinctive trait in invertebrate reggie genes, is presented.
Received: 24 January 2001 / Accepted: 27 July 2001 相似文献
2.
The Evolutionary History of Prosaposin: Two Successive Tandem-Duplication Events Gave Rise to the Four Saposin Domains in Vertebrates 总被引:1,自引:0,他引:1
Einat Hazkani-Covo Neta Altman Mia Horowitz Dan Graur 《Journal of molecular evolution》2002,54(1):30-34
Prosaposin is a multifunctional protein encoded by a single-copy gene. It contains four saposin domains (A, B, C, and D)
occurring as tandem repeats connected by linker sequences. Because the saposin domains are similar to one another, it is deduced
that they were created by sequential duplications of an ancestral domain. There are two types of evolutionary scenarios that
may explain the creation of the four-domain gene: (1) two rounds of tandem internal gene duplication and (2) three rounds
of duplications. An evolutionary and phylogenetic analysis of saposin DNA and amino acid sequences from human, mouse, rat,
chicken, and zebrafish indicates that the first evolutionary scenario is the most likely. Accordingly, an ancestral saposin-unit
duplication produced a two-domain gene, which, subsequently, underwent a second complete tandem duplication to give rise to
the present four-domain structure of the prosaposin gene.
Received: 8 February 2001 / Accepted: 29 June 2001 相似文献
3.
In this paper we analyzed 49 lactate dehydrogenase (LDH) sequences, mostly from vertebrates. The amino acid sequence differences
were found to be larger for a human–killifish pair than a human–lamprey pair. This indicates that some protein sequence convergence
may occur and reduce the sequence differences in distantly related species. We also examined transitions and transversions
separately for several species pairs and found that the transitions tend to be saturated in the distantly related species
pair, while transversions are increasing. We conclude that transversions maintain a conservative rate through the evolutionary
time. Kimura's two-parameter model for multiple-hit correction on transversions only was used to derive a distance measure
and then construct a neighbor-joining (NJ) tree. Three findings were revealed from the NJ tree: (i) the branching order of
the tree is consistent with the common branch pattern of major vertebrates; (ii) Ldh-A and Ldh-B genes were duplicated near the origin of vertebrates; and (iii) Ldh-C and Ldh-A in mammals were produced by an independent gene duplication in early mammalian history. Furthermore, a relative rate test
showed that mammalian Ldh-C evolved more rapidly than mammalian Ldh-A. Under a two-rate model, this duplication event was calibrated to be approximately 247 million years ago (mya), dating back
to the Triassic period. Other gene duplication events were also discovered in Xenopus, the first duplication occurring approximately 60–70 mya in both Ldh-A and Ldh-B, followed by another recent gene duplication event, approximately 20 mya, in Ldh-B.
Received: 5 October 2001 / Accepted: 24 October 2001 相似文献
4.
Biglycan and decorin are two members of a family of small extracellular matrix proteoglycans characterized by the presence
of 10 leucine-rich repeats and one or two attachment sites for glucosaminoglycans. Both have thus far been described only
from tetrapod species, mainly mammals. Because the extracellular matrix has played an important part in the evolution of Metazoa,
the phylogeny of its components is of considerable interest. In this study, biglycan-like (BGL) cDNA sequences have been obtained
from two teleost (Oreochromis cichlid and zebrafish) and two lamprey species. The analysis of the sequences suggests that, like tetrapods, the lampreys
possess two types of proteoglycans, both of which are biglycan-like; decorin-like proteoglycans could not be identified in
these species. The genes specifying these two types apparently arose by duplication in the lamprey lineage after its divergence
from gnathostomes. The two teleost species possess a BGL proteoglycan and a bona fide decorin. The BGL proteoglycan is highly
divergent from the tetrapod biglycan and related to the BGL proteoglycans of the lamprey. Hence, although the duplication
generating the ancestors of biglycan and decorin genes occurred after the divergence of agnathans but before the emergence
of teleosts, only decorin acquired its characteristic properties in the bony fishes. The BGL gene presumably turned into a typical biglycan only in the tetrapod lineages. The presumed acquisitions of new functions
appear to have been accompanied by changes in the evolutionary rate.
Received: 13 April 2000 / Accepted: 4 July 2000 相似文献
5.
A comprehensive analysis of duplication and gene conversion for 7394 Caenorhabditis elegans genes (about half the expected total for the genome) is presented. Of the genes examined, 40% are involved in duplicated
gene pairs. Intrachromosomal or cis gene duplications occur approximately two times more often than expected. In general the closer the members of duplicated
gene pairs are, the more likely it is that gene orientation is conserved. Gene conversion events are detectable between only
2% of the duplicated pairs. Even given the excesses of cis duplications, there is an excess of gene conversion events between cis duplicated pairs on every chromosome except the X chromosome. The relative rates of cis and trans gene conversion and the negative correlation between conversion frequency and DNA sequence divergence for unconverted regions
of converted pairs are consistent with previous experimental studies in yeast. Three recent, regional duplications, each spanning
three genes are described. All three have already undergone substantial deletions spanning hundreds of base pairs. The relative
rates of duplication and deletion may contribute to the compactness of the C. elegans genome.
Received: 30 July 1998 / Accepted: 12 October 1998 相似文献
6.
Maximum Likelihood Estimation on Large Phylogenies and Analysis of Adaptive Evolution in Human Influenza Virus A 总被引:1,自引:0,他引:1
Yang Z 《Journal of molecular evolution》2000,51(5):423-432
Algorithmic details to obtain maximum likelihood estimates of parameters on a large phylogeny are discussed. On a large tree,
an efficient approach is to optimize branch lengths one at a time while updating parameters in the substitution model simultaneously.
Codon substitution models that allow for variable nonsynonymous/synonymous rate ratios (ω=d
N/d
S) among sites are used to analyze a data set of human influenza virus type A hemagglutinin (HA) genes. The data set has 349
sequences. Methods for obtaining approximate estimates of branch lengths for codon models are explored, and the estimates
are used to test for positive selection and to identify sites under selection. Compared with results obtained from the exact
method estimating all parameters by maximum likelihood, the approximate methods produced reliable results. The analysis identified
a number of sites in the viral gene under diversifying Darwinian selection and demonstrated the importance of including many
sequences in the data in detecting positive selection at individual sites.
Received: 25 April 2000 / Accepted: 24 July 2000 相似文献
7.
Multigene families and the evolution of complexity 总被引:20,自引:0,他引:20
Tomoko Ohta 《Journal of molecular evolution》1991,33(1):34-41
Summary Higher organisms are complex, and their developmental processes are controlled by the sequential expression of genes that often form multigene families. Facts are surveyed on how functional diversity of genes is related to duplication of genes or segments of genes, by emphasizing that diversity is often enhanced by alternate splicing and proteolytic cleavage involving duplicated genes or gene segments. Analyses of a population genetics model for the origin of gene families suggest that positive Darwinian selection is needed for acquiring gene families with desirable functions. Based on these considerations, examples that show acceleration of amino acid substitution relative to synonymous change during evolutionary processes are surveyed. Some of such examples strongly suggest that positive selection has worked. In other cases it is difficult to judge whether or not acceleration is caused by positive Darwinian selection. As a general pattern, acceleration of amino acid substitution is often found to be related to gene duplication. It is thought that complexity and diversity of gene function have been advantageous in the long evolutionary course of higher organisms. 相似文献
8.
António M. Baptista Per Harald Jonson Edward Hough Steffen B. Petersen 《Journal of molecular evolution》1998,47(3):353-362
The trypsin family of serine proteases is one of the most studied protein families, with a wealth of amino acid sequence
information available in public databases. Since trypsin-like enzymes are widely distributed in living organisms in nature,
likely evolutionary scenarios have been proposed. A novel methodology for Fourier transformation of biological sequences (FOTOBIS)
is presented. The methodology is well suited for the identification of the size and extent of short repeats in protein sequences.
In the present paper the trypsin family of enzymes is analyzed with FOTOBIS and strong evidence for tandem gene duplication
is found. A likely evolutionary path for the development of present-day trypsins involved an intrinsic extensive tandem gene
duplication of a small DNA fragment of 15–18 nucleotides, corresponding to five or six amino acids. This ancestral trypsin
gene was subsequently duplicated, leading to the earliest version of a full-sized trypsin, from which the contemporary trypsins
have developed.
Received: 22 November 1997 / Accepted: 26 January 1998 相似文献
9.
The pairs of nitrogen fixation genes nifDK and nifEN encode for the α and β subunits of nitrogenase and for the two subunits of the NifNE protein complex, involved in the biosynthesis
of the FeMo cofactor, respectively. Comparative analysis of the amino acid sequences of the four NifD, NifK, NifE, and NifN
in several archaeal and bacterial diazotrophs showed extensive sequence similarity between them, suggesting that their encoding
genes constitute a novel paralogous gene family. We propose a two-step model to reconstruct the possible evolutionary history
of the four genes. Accordingly, an ancestor gene gave rise, by an in-tandem paralogous duplication event followed by divergence,
to an ancestral bicistronic operon; the latter, in turn, underwent a paralogous operon duplication event followed by evolutionary
divergence leading to the ancestors of the present-day nifDK and nifEN operons. Both these paralogous duplication events very likely predated the appearance of the last universal common ancestor.
The possible role of the ancestral gene and operon in nitrogen fixation is also discussed.
Received: 21 June 1999 / Accepted: 1 March 2000 相似文献
10.
In translation, separate aminoacyl-tRNA synthetases attach the 20 different amino acids to their cognate tRNAs, with the
exception of glutamine. Eukaryotes and some bacteria employ a specific glutaminyl-tRNA synthetase (GlnRS) which other Bacteria,
the Archaea (archaebacteria), and organelles apparently lack. Instead, tRNAGln is initially acylated with glutamate by glutamyl-tRNA synthetase (GluRS), then the glutamate moiety is transamidated to glutamine.
Lamour et al. [(1994) Proc Natl Acad Sci USA 91:8670–8674] suggested that an early duplication of the GluRS gene in eukaryotes
gave rise to the gene for GlnRS—a copy of which was subsequently transferred to proteobacteria. However, questions remain
about the occurrence of GlnRS genes among the Eucarya (eukaryotes) outside of the ``crown' taxa (animals, fungi, and plants),
the distribution of GlnRS genes in the Bacteria, and their evolutionary relationships to genes from the Archaea. Here, we
show that GlnRS occurs in the most deeply branching eukaryotes and that putative GluRS genes from the Archaea are more closely
related to GlnRS and GluRS genes of the Eucarya than to those of Bacteria. There is still no evidence for the existence of
GlnRS in the Archaea. We propose that the last common ancestor to contemporary cells, or cenancestor, used transamidation
to synthesize Gln-tRNAGln and that both the Bacteria and the Archaea retained this pathway, while eukaryotes developed a specific GlnRS gene through
the duplication of an existing GluRS gene. In the Bacteria, GlnRS genes have been identified in a total of 10 species from
three highly diverse taxonomic groups: Thermus/Deinococcus, Proteobacteria γ/β subdivision, and Bacteroides/Cytophaga/Flexibacter.
Although all bacterial GlnRS form a monophyletic group, the broad phyletic distribution of this tRNA synthetase suggests that
multiple gene transfers from eukaryotes to bacteria occurred shortly after the Archaea–eukaryote divergence. 相似文献
11.
Analysis of the 18S rDNA sequences of five species of the family Dugesiidae (phylum Platyhelminthes, suborder Tricladida,
infraorder Paludicola) and eight species belonging to families Dendrocoelidae and Planaridae and to the infraorder Maricola
showed that members of the family Dugesiidae have two types of 18S rDNA genes, while the rest of the species have only one.
The duplication event also affected the ITS-1, 5.8S, ITS-2 region and probably the 28S gene. The mean divergence value between
the type I and the type II sequences is 9% and type II 18S rDNA genes are evolving 2.3 times more rapidly than type I. The
evolutionary rates of type I and type II genes were calibrated from biogeographical data, and an approximate date for the
duplication event of 80–120 million years ago was calculated. The type II gene was shown, by RT-PCR, to be transcribed in
adult individuals of Schmidtea polychroa, though at very low levels. This result, together with the fact that most of the functionally important positions for small-subunit
rRNA in prokaryotes have been conserved, indicates that the type II gene is probably functional.
Received: 24 March 1998 / Accepted: 17 March 1999 相似文献
12.
Suga H Koyanagi M Hoshiyama D Ono K Iwabe N Kuma K Miyata T 《Journal of molecular evolution》1999,48(6):646-653
To know whether genes involved in cell–cell communication typical of multicellular animals dramatically increased in concert
with the Cambrian explosion, the rapid evolutionary burst in the major groups of animals, and whether these genes exist in
the sponge lacking cell cohesiveness and coordination typical of eumetazoans, we have carried out cloning of the G-protein
α subunit (Gα) and the protein tyrosine kinase (PTK) cDNAs from Ephydatia fluviatilis (freshwater sponge) and Hydra magnipapillata strain 105 (hydra). We obtained 13 Gα and 20 PTK cDNAs. Generally animal gene families diverged first by gene duplication
(subtype duplication) that gave rise to diverse subtypes with different primary functions, followed by further gene duplication
in the same subtype (isoform duplication) that gave rise to isoform genes with virtually identical function. Phylogenetic
trees of Gα and PTK families including cDNAs from sponge and hydra revealed that most of the present-day subtypes had been
established in the very early evolution of animals before the parazoan–eumetazoan split, the earliest branching among the
extant animal phyla, by extensive subtype duplication: for PTK and Gα families, 23 and 9 subtype duplications were observed
in the early stage before the parazoan–eumetazoan split, respectively, and after that split, only 2 and 1 subtype duplications
were found, respectively. After the separation from arthropods, vertebrates underwent frequent isoform duplications before
the fish–tetrapod split. Furthermore, rapid amino acid changes appear to have occurred in concert with the extensive subtype
duplication and isoform duplication. Thus the pattern of gene diversification during animal evolution might be characterized
by bursts of gene duplication interrupted by considerably long periods of silence, instead of proceeding gradually, and there
might be no direct link between the Cambrian explosion and the extensive gene duplication that generated diverse functions
(subtypes) of these families.
Received: 4 November 1998 / Accepted: 17 November 1998 相似文献
13.
While globin genes ctt-2β and ctt-9.1 in Chironomus thummi thummi each have a single intron, all of the other insect globin genes reported so far are intronless. We analyzed four globin genes
linked to the two intron-bearing genes in C. th. thummi. Three have a single intron at the same position as ctt-2β and ctt-9.1; the fourth is intronless and lies between intron bearing genes. Finally, in addition to its intron, one gene (ctt-13RT) was recently interrupted by retrotransposition. Phylogenetic analyses show that the six genes in C. th. thummi share common ancestry with five globin genes in the distantly related species C. tentans, and that a 5-gene ancestral cluster predates the divergence of the two species. One gene in the ancestral cluster gave rise
to ctn-ORFB in C. tentans, and duplicated in C. th. thummi to create ctt-11 and ctt-12. From parsimonious calculations of evolutionary distances since speciation, ctt-11, ctt-12, and ctn-ORFB evolved rapidly, while ctn-ORFE in C. tentans evolved slowly compared to other globin genes in the clusters. While these four globins are under selective pressure, we
suggest that most chironomid globin genes were not selected for their unique function. Instead, we propose that high gene
copy number itself was selected because conditions favored organisms that could synthesize more hemoglobin. High gene copy
number selection to produce more of a useful product may be the basis of forming multigene families, all of whose members
initially accumulate neutral substitutions while retaining essential function. Maintenance of a large family of globin genes
not only ensured high levels of hemoglobin production, but may have facilitated the extensive divergence of chironomids into
as many as 5000 species.
Received: 31 December 1996 / Accepted: 16 May 1997 相似文献
14.
We previously sequenced two regions around the centromeric end of HLA class I and the boundary between class I and class
III. In this paper we analyze the two regions of about 385 kb and confirm, giving a new line of evidence, that the following
two pairs of the genomic segments were duplicated in evolution: (i) a 43-kb genomic segment including the HLA-B gene showing
the highest polymorphism among the classical HLA class I loci (class Ia) and a 40-kb segment including the HLA-C locus showing
the lowest polymorphism and (ii) a 52-kb segment including the MIC (MHC class I chain related gene) B and a 35-kb segment
including MICA. We also found that repetitive elements such as SINEs, LINEs, and LTRs occupy as much as 47% of nucleotides
in this 385-kb region. This unusually high content of repetitive elements indicates that repeat-mediated rearrangements have
frequently occurred in the evolutionary history of the HLA class Ia region. Analysis of LINE compositions within the two pairs
of duplicated segments revealed that (i) LINEs in these regions had been dispersed prior to both the duplication of the HLA-B
and -C loci and the duplication of the MICB and MICA loci, and (ii) the divergence of the HLA-B and -C loci occurred prior
to the duplication of the MICA and MICB loci. To find novel genes responsible for HLA class I-associated or other diseases,
we performed computer analysis applying GenScan and GRAIL to GenBank's dbEST. As a result, at least five as yet uncharacterized
genes were newly mapped on the HLA class I centromeric region studied. These novel genes should be analyzed further to determine
their relationships to diseases associated with this region.
Received: 16 June 1998 / Accepted: 18 August 1998 相似文献
15.
Langenkämper G Fung RW Newcomb RD Atkinson RG Gardner RC MacRae EA 《Journal of molecular evolution》2002,54(3):322-332
We present phylogenetic analyses to demonstrate that there are three families of sucrose phosphate synthase (SPS) genes present
in higher plants. Two data sets were examined, one consisting of full-length proteins and a second larger set that covered
a highly conserved region including the 14-3-3 binding region and the UDPGlu active site. Analysis of both datasets showed
a well supported separation of known genes into three families, designated A, B, and C. The genomic sequences of Arabidopsis thaliana include a member in each family: two genes on chromosome 5 belong to Family A, one gene on chromosome 1 to Family B, and
one gene on chromosome 4 to Family C. Each of three Citrus genes belong to one of the three families. Intron/exon organization of the four Arabidopsis genes differed according to phylogenetic analysis, with members of the same family from different species having similar
genomic organization of their SPS genes. The two Family A genes on Arabidopsis chromosome 5 appear to be due to a recent duplication. Analysis of published literature and ESTs indicated that functional
differentiation of the families was not obvious, although B family members appear not to be expressed in roots. B family genes
were cloned from two Actinidia species and southern analysis indicated the presence of a single gene family, which contrasts to the multiple members of
Family A in Actinidia. Only two family C genes have been reported to date.
Received: 17 April 2001 / Accepted: 27 August 2001 相似文献
16.
Evolution of MADS-box gene induction by FLO/LFY genes 总被引:2,自引:0,他引:2
Himi S Sano R Nishiyama T Tanahashi T Kato M Ueda K Hasebe M 《Journal of molecular evolution》2001,53(4-5):387-393
Some MADS-box genes function as floral homeotic genes. The Arabidopsis LFY gene is a positive regulator of floral homeotic genes, and homologs of the FLO/LFY gene family in other angiosperms and gymnosperms are likely to have a similar function. To investigate the origin of the
floral homeotic gene regulatory cascade involving the FLO/LFY gene, FLO/LFY homologs were cloned from a leptosporangiate fern (Ceratopteris richardii), two eusporangiate ferns (Angiopteris lygodiifolia and Botrychium multifidum var. robustum), three fern allies (Psilotum nudum, Equisetum arvense, and Isoetes asiatica), and a moss (Physcomitrella patens). The FLO/LFY gene phylogenetic tree indicates that both duplication and loss of FLO/LFY homologs occurred during the course of vascular plant evolution. The expression patterns of the Ceratopteris LFY genes (CrLFY1 and 2) were assessed. CrLFY1 expression was prominent in tissues including shoot tips and circinate reproductive leaves, but very weak in other tissues
examined. Expression of CrLFY2 was also prominent in tissues, including shoot tips and circinate reproductive leaves. These patterns of expression are dissimilar
to that of any Ceratopteris MADS-box gene previously reported, suggesting that the induction of MADS-box genes by FLO/LFY is not established at the stage of ferns.
Received: 4 January 2001 / Accepted: 28 February 2001 相似文献
17.
Karen D. Crow Chris T. Amemiya Jutta Roth Günter P. Wagner 《Evolution; international journal of organic evolution》2009,63(6):1574-1592
Gene duplication is widely regarded as the predominant mechanism by which genes with new functions and associated phenotypic novelties arise. A whole genome duplication occurred shortly before the most recent common ancestor of teleosts, the most diverse chordate group, resulting in duplication and retention of many Hox cluster genes. Because they play a key role in determination of body plan morphology, it has been widely assumed that Hox genes play a key role in the evolution of diverse metazoan body plans. However, it is not clear whether certain aspects of molecular evolution, such as asymmetric divergence and neofunctionalization, contribute to the initial retention of paralogs. We investigate the molecular evolution and functional divergence of the duplicated HoxA13 paralogs in zebrafish to determine when asymmetric divergence and functional divergence occurred after the duplication event. Our findings demonstrate the contribution of gene duplication to the evolution of novel features through evolutionary mechanisms other than those traditionally investigated, such as positive selection occurring immediately after gene duplication. Rather, we find a latent build up of molecular changes in a gene associated with the development of a novel feature in a very diverse group of fishes. 相似文献
18.
Jerzy K. Kulski Silvana Gaudieri Annalise Martin Roger L. Dawkins 《Journal of molecular evolution》1999,49(1):84-97
The recent availability of genomic sequence information for the class I region of the MHC has provided an opportunity to
examine the genomic organization of HLA class I (HLAcI) and PERB11/MIC genes with a view to explaining their evolution from
the perspective of extended genomic duplications rather than by simple gene duplications and/or gene conversion events. Analysis
of genomic sequence from two regions of the MHC (the alpha- and beta-blocks) revealed that at least 6 PERB11 and 14 HLAcI
genes, pseudogenes, and gene fragments are contained within extended duplicated segments. Each segment was searched for the
presence of shared (paralogous) retroelements by RepeatMasker in order to use them as markers of evolution, genetic rearrangements,
and evidence of segmental duplications. Shared Alu elements and other retroelements allowed the duplicated segments to be
classified into five distinct groups (A to E) that could be further distilled down to an ancient preduplication segment containing
a HLA and PERB11 gene, an endogenous retrovirus (HERV-16), and distinctive retroelements. The breakpoints within and between
the different HLAcI segments were found mainly within the PERB11 and HLA genes, HERV-16, and other retroelements, suggesting
that the latter have played a major role in duplication and indel events leading to the present organization of PERB11 and
HLAcI genes. On the basis of the features contained within the segments, a coevolutionary model premised on tandem duplication
of single and multipartite genomic segments is proposed. The model is used to explain the origins and genomic organization
of retroelements, HERV-16, DNA transposons, PERB11, and HLAcI genes as distinct segmental combinations within the alpha- and
beta-blocks of the human MHC.
Received: 5 December 1998 / Accepted: 27 January 1999 相似文献
19.
Singhania NA Dyer KD Zhang J Deming MS Bonville CA Domachowske JB Rosenberg HF 《Journal of molecular evolution》1999,49(6):721-728
The two eosinophil ribonucleases, eosinophil-derived neurotoxin (EDN/RNase 2) and eosinophil cationic protein (ECP/RNase
3), are among the most rapidly evolving coding sequences known among primates. The eight mouse genes identified as orthologs
of EDN and ECP form a highly divergent, species-limited cluster. We present here the rat ribonuclease cluster, a group of
eight distinct ribonuclease A superfamily genes that are more closely related to one another than they are to their murine
counterparts. The existence of independent gene clusters suggests that numerous duplications and diversification events have
occurred at these loci recently, sometime after the divergence of these two rodent species (∼10–15 million years ago). Nonsynonymous
substitutions per site (d
N) calculated for the 64 mouse/rat gene pairs indicate that these ribonucleases are incorporating nonsilent mutations at accelerated
rates, and comparisons of nonsynonymous to synonymous substitution (d
N / d
S) suggest that diversity in the mouse ribonuclease cluster is promoted by positive (Darwinian) selection. Although the pressures
promoting similar but clearly independent styles of rapid diversification among these primate and rodent genes remain uncertain,
our recent findings regarding the function of human EDN suggest a role for these ribonucleases in antiviral host defense.
Received: 8 April 1999 / Accepted: 22 June 1999 相似文献
20.
Tandemly duplicated actin genes have been isolated from a Helicoverpa armigera genomic library. Sequence comparisons with actin genes from other species suggest they encode cytoplasmic actins, being most
closely related to the Bombyx mori A3 actin gene. The duplicated H. armigera actin genes, termed A3a and A3b, share 98.3% nucleotide sequence identity over their entire putative coding region. Analysis
of the distribution of nucleotide differences shows the first 763 bp are identical between the two coding regions, with the
18 nucleotide changes occurring in the remaining 366 bp. This observation suggests a gene conversion event has taken place
between the duplicated H. armigera A3a and A3b actin genes. Translation of the open-reading frames indicates the products of these genes are identical, apart
from a single amino acid difference at codon 273. Polymerase chain reaction and northern blot analysis have shown both H. armigera A3a and A3b genes are expressed during pupal development and in the brain of newly eclosed adults. A region 5′ of the H. armigera A3a actin gene start codon has been identified which contains regulatory sequences commonly found in the promoter region
of actin genes, including TATA, CAAT, and CArG motifs.
Received: 10 January 1996 / Accepted: 12 March 1996 相似文献