Evolution of the rabbit immunoglobulin κ chain genes

We have analyzed the organization and the structure of rabbit chain genes encoding b allotypes in wild rabbits. The 1 gene of the b95 allotype was cloned and its structure determined. The J region is composed of five segments but only J2 appears to be functional and is identical to the J2 segment of the b4 allotype. The J region is highly conserved among the various b allotypes, whereas the constant region exon displays a high level of differences when compared with other allotypes (9%–30% of different amino acids). The b95 J region is closer to that of b4^var and the constant region to b5 allotype constant region. Alignment of nucleotide sequences revealed that the constant region exon displays segmental similarities with b4 and bas constant regions. The mosaic structure of b95 allotype gene indicates that complex allotypes of 1 genes may result from genetic exchanges of gene conversion between the different genes.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide database and have been assigned the accession number M22542. Address correspondence and offprint requests to: P.-A. Cazenave.     

Duplication and divergence of the genes of the α-esterase cluster ofDrosophila melanogaster

The α-esterase cluster of D. melanogaster contains 11 esterase genes dispersed over 60 kb. Embedded in the cluster are two unrelated open reading frames that have sequence similarity with genes encoding ubiquitin-conjugating enzyme and tropomyosin. The esterase amino acid sequences show 37–66% identity with one another and all but one have all the motifs characteristic of functional members of the carboxyl/cholinesterase multigene family. The exception has several frameshift mutations and appears to be a pseudogene. Patterns of amino acid differences among cluster members in relation to generic models of carboxyl/cholinesterase protein structure are broadly similar to those among other carboxyl/cholinesterases sequenced to date. However the α-esterases differ from most other members of the family in: their lack of a signal peptide; the lack of conservation in cysteines involved in disulfide bridges; and in four indels, two of which occur in or adjacent to regions that align with proposed substrate-binding sites of other carboxyl/cholinesterases. Phylogenetic analyses clearly identify three simple gene duplication events within the cluster. The most recent event involved the pseudogene which is located in an intron of another esterase gene. However, relative rate tests suggest that the pseudogene remained functional after the duplication event and has become inactive relatively recently. The distribution of indels also suggests a deeper node in the gene phylogeny that separates six genes at the two ends of the cluster from a block of five in the middle. Received: 18 January 1996 / Accepted: 12 March 1996     

Chromosomal arrangement of the chicken β-type globin genes

We have isolated the chicken β-type globin genes from a library of chicken DNA-λ Charon 4A recombinant bacteriophage. There are four β-type genes within this segment of the genome; we believe this represents all of the β-type genes of the chicken. The recombinant λCβG1 contains the embryonic ?- and adult β-globin genes. The hatching β^H and embryonic p-globin genes are found in the recombinant λCβG2. Although λCβG1 and λCβG2 do not physically overlap, we present evidence that all four genes are closely linked and transcribed from the same DNA strand. These experiments demonstrate that the chromosomal regions represented by λCβG1 and λCβG2 lie approximately 1.6 kb apart in the chicken genome. A third recombinant λCβG3 extends the genomic locus studied in the vicinity of the β-type globin genes to approximately 39 kb. The physical order of the chicken β-type globin genes within this segment of the chromosome is 5′ … ?-β^H-β-? … 3′. This arrangement is unique among the vertebrate β-type globin gene clusters thus far examined, in that embryonic genes are located at the 5′ and 3′ ends of the cluster while the hatching and adult genes occupy central positions.     

Physicochemical measurement of the base composition of mRNA-related sequences of the human α and β globin genes

Hybrids formed between human and globin cDNA and total human cellular DNA have been studied by thermal denaturation and cesium chloride density gradient centrifugation. From these studies, the weight average G+C content of human globin cDNA has been determined to be 62%±2% and that of human globin cDNA 51%±2%. These values correlate well with the results of G+C content of the human and globin cDNAs as determined by direct nucleotide sequence analysis of the cDNAs. Thermal denaturation and cesium chloride density gradient centrifugation of DNA-cDNA hybrids can therefore provide accurate information on the base composition of mRNA related sequences of any single copy gene for which a relatively pure cDNA can be obtained, without the necessity for direct nucleotide sequence analysis.     

Does the evolutionary history of aminoacyl-tRNA synthetases explain the loss of mitochondrial tRNA genes?

The importation of cytosolic tRNAs is required for protein synthesis in the mitochondria of the wide variety of eukaryotes that lack a complete set of mitochondrial tRNA genes. The evolutionary history of the process, however, is still enigmatic. The analysis presented here suggests that the loss of distinct mitochondrial tRNA genes was not random and that it might be explained by the differential capabilities of mitochondrial aminoacyl-tRNA synthetases to charge imported eukaryotic-type tRNAs with amino acid.     

Cloning,characterisation and expression of the α-tubulin genes of the leech,Hirudo medicinalis

We have isolated two α-tubulin cDNAs from the leech, Hirudo medicinalis. Both encode putative proteins of 451 amino-acids which differ from each other at only two positions. Southern blotting suggests that there are only two α-tubulin genes in the leech. The genes contain two introns and, because of the extremely high homology of the nucleotide sequence from the second intron to the end of the genes, we have inferred that a gene conversion event about 9.5 million years ago has homogenised the Hirudo α-tubulin sequences. Using in situ hybridisation to tissue sections, we have shown that the two genes are probably expressed in all neurons of the leech ganglia and that their spatial distribution remains unchanged during neuronal regeneration. The deduced amino-acid sequences of the leech α-tubulins show that they have greatest similarity to those from a platyhelminth, echiuran and mollusc with rather less to arthropod α-tubulins. The protein sequences of the leech α-tubulins have been compared with representatives of those from across all phyla to determine if any specific feature labels certain isotypes of tubulin for neuronal expression.     

Disruption of genes for the enhanced biosynthesis of α-ketoglutarate in Corynebacterium glutamicum

The development of microbial strains for the enhanced production of α-ketoglutarate (α-KG) was investigated using a strain of Corynebacterium glutamicum that overproduces of l-glutamate, by disrupting three genes involved in the α-KG biosynthetic pathway. The pathways competing with the biosynthesis of α-KG were blocked by knocking out aceA (encoding isocitrate lyase, ICL), gdh (encoding glutamate dehydrogenase, l-gluDH), and gltB (encoding glutamate synthase or glutamate-2-oxoglutarate aminotransferase, GOGAT). The strain with aceA, gltB, and gdh disrupted showed reduced ICL activity and no GOGAT and l-gluDH activities, resulting in up to 16-fold more α-KG production than the control strain in flask culture. These results suggest that l-gluDH is the key enzyme in the conversion of α-KG to l-glutamate; therefore, prevention of this step could promote α-KG accumulation. The inactivation of ICL leads the carbon flow to α-KG by blocking the glyoxylate pathway. However, the disruption of gltB did not affect the biosynthesis of α-KG. Our results can be applied in the industrial production of α-KG by using C. glutamicum as producer.     

Sequence analysis of a variety of primate fertilin α genes: Evidence for non-functional genes in the gorilla and man

The sperm surface fertilin complex was first described in the guinea pig where it was found as a heterodimer of α and β subunits, both of which were proposed to play a role in sperm-oolemma recognition and plasma membrane fusion during fertilisation. Whilst the β subunit is apparently testis-specific, the finding of low levels of fertilin α in nonreproductive tissues has cast some doubt on a unique role in fertilisation. Moreover, the absence of a functional fertilin α gene in the human would imply that this gene product is not absolutely essential for fertilisation, although it could play a facilitatory role. We now describe the organisation and sequence of the fertilin α genes in a range of primates, including the great apes, and find that the gorilla gene, like that of the human, is non-functional. Mol. Reprod. Dev. 51:92–97, 1998. © 1998 Wiley-Liss, Inc.     

Evolution of the human sarcomeric-actin genes: Evidence for units of selection within the 3′ untranslated regions of the mRNAs

Summary The complete 3 untranslated region (3UTR) sequence of the human skeletal-actin gene has been compared with the corresponding regions of the rat and chicken skeletal-actin genes. This comparison reveals that the skeletal-actin 3UTR is composed of conserved and nonconserved segments. By using genomic Southern transfer blots and thermal stability (T_m) measurements, we found that the cardiac-actin gene 3UTR also consists of conserved and nonconserved segments. Comparison of human andXenopus laevis cardiac-actin mRNA sequences confirms the presence of a region of high similarity in the 3UTR. We conclude that subsegments of the 3UTRs of both skeletal- and cardiac-actin genes of birds and mammals are under considerable selective pressure. This suggests that these conserved sequences may have functional roles in actin-gene expression or regulation, and that these roles might be different for each actin isoform.     

Superfamily of α-galactosidase MEL genes of the Saccharomyces sensu stricto species complex

In order to study the molecular evolution of the yeasts grouped in the Saccharomyces sensu stricto species complex by analysis of the MEL gene family, we have cloned and sequenced two new species-specific MEL genes from Saccharomyces yeasts: S. paradoxus (MELp) and a Japanese Saccharomyces sp. (MELj). The clones were identified by sequence homology to the S. cerevisiae MEL1 gene. Both clones revealed an ORF of 1413 bp coding for a protein of 471 amino acids. The deduced molecular weights of the α-galactosidase enzymes were 52 767 for MELp and 52 378 for MELj. The nucleotide sequences of the MELp (EMBL accession no. X95505) and the MELj (EMBL accession no. X95506) genes showed 74.7% identity. The degree of identity of MELp to the MEL1 gene was 76.8% and to the S. pastorianus MELx gene, 75.7%. The MELj coding sequence was 75.1% identical to the MEL1 gene and 80.7% to the MELx gene. The data suggest that MEL1, MELj, MELp, and MELx genes are species-specific MEL genes. The strains studied each have only one MEL locus. The MELp gene is located on the S. paradoxus equivalent of S. cerevisiae chromosome X; the MELj gene was on the chromosome that comigrates with the S. cerevisiae chromosome VII/XV doublet and hybridizes to the S. cerevisiae chromosome XV marker HIS3.     

Pollen as a vehicle for the escape of engineered genes?

Recent studies of pollen exchange between neighboring populations of plants have shown that interpopulation gene flow can proceed over much greater distances and at higher rates than hitherto believed. This means that the escape of engineered genes from crop plants to their wild relatives is not only possible, but also likely. The development of containment strategies, such as extra modifications for increased self-fertilization and decreased pollen longevity in engineered crop plants, will be necessary to safeguard against such escape.