A pseudogene cluster in the leader region of the Euglena chloroplast 16S-23S rRNA genes.

The nucleotide sequence of a region (leader region) preceding the 5'-end of 16S-23S rRNA gene region of Euglena gracilis chloroplast DNA was compared with the homologous sequences that code for the 16S-23S rRNA operons of Euglena and E. coli. The leader region shows close homology in sequence to the 16S-23S rRNA gene region of Euglena (Orozco et al. (1980) J. Biol.Chem. 255, 10997-11003) as well as to the rrnD operon of E. coli, suggesting that it was derived from the 16S-23S rRNA gene region by gene duplication. It was shown that the leader region had accumulated nucleotide substitutions at an extremely rapid rate in its entirety, similar to the rate of tRNAIle pseudogene identified in the leader region. In addition, the leader region shows an unique base content which is quite distinct from those of 16S-23S rRNA gene regions of Euglena and E. coli, but again is similar to that of the tRNAIle pseudogene. The above two results strongly suggest that the leader region contains a pseudogene cluster which was derived from a gene cluster coding for the functional 16S-23S rRNA operon possibly by imperfect duplication during evolution of Euglena chloroplast DNA.     

The Z family, a group of transposed human immunoglobulin V kappa genes

A group of highly homologous transposed human V kappa I genes, which we call the Z family, was characterized. To date four members, ZI-ZIV, comprising about 230 kb, have been analyzed on cosmid clones. The largest region (ZI) has a length of 85 kb. The Z regions show extensive homology to each other according to restriction maps and hybridization data. In each Z region a solitary V kappa I gene was found. No V kappa genes of other subgroups were detected by hybridization. The nucleotide sequence of the ZI gene revealed a non-processed V kappa I pseudogene. Hybridization experiments with DNAs from rodent/human cell hybrids and other experimental data indicate that some and possibly all members of the Z family lie outside of the kappa locus which is located on chromosome 2; they have been transposed to other chromosomes. Because of their separation from the J kappa C kappa gene segment, the Z genes can be classified as pseudogenes independent of their sequences. We postulate that the Z family arose by amplification event(s). The Z regions can also be regarded as a small family of very long repetitive sequences.     

Examination of four HLA class I pseudogenes. Common events in the evolution of HLA genes and pseudogenes.

The HLA class I gene family in lymphoblastoid cell line 721 has been studied in detail and a number of sequences in addition to the classical genes have been identified. The cloning, characterization, and nucleotide sequences of four sequences, all full length HLA class I pseudogenes, are described in this report. These pseudogenes, contained within 5.4-, 5.9-, 7.0-, and 9.2-kb HindIII fragments, each have the class I exon-intron structure as well as class I homology in their 5' and 3' flanking regions. However, all four sequences have one or more substitutions that perturb the coding region, leaving little doubt that they are in fact pseudogenes. Comparisons among these sequences and the HLA class I genes revealed that their homology with the class I genes is patchwork. Thus, although some regions have diverged, other contiguous intron-exon sequences are highly conserved. Comparisons in the 5' regions indicate that the pseudogene promoters more closely resemble the classical HLA promoters than the nonclassical promoters as none of the unique structural features found in the HLA-E, -F, or -G regulatory regions are present in any of the pseudogene promoters. Further comparisons revealed that at least two putative gene conversion events, similar to those hypothesized to have occurred in the evolution of some HLA genes, may have occurred in the evolution of some of the pseudogenes. These and other hypothetical events in the evolution of the class I gene family are discussed.     

Molecular Analysis of the Hot Spot Region Related to Length Mutations in Wheat Chloroplast Dnas. I. Nucleotide Divergence of Genes and Intergenic Spacer Regions Located in the Hot Spot Region

The nucleotide divergence of chloroplast DNAs around the hot spot region related to length mutation in Triticum (wheat) and Aegilops was analyzed. DNA sequences (ca. 4.5 kbp) of three chloroplast genome types of wheat complex were compared with one another and with the corresponding region of other grasses. The sequences region contained rbcL and psaI, two open reading frames, and a pseudogene, rpl23' (pseudogene for ribosomal protein L23) disrupted by AT-rich intergic spacer regions. The evolution of these genes in the closely related wheat complex is characterized by nonbiased nucleotide substitutions in terms of being synonymous/nonsynonymous, having A-T pressure transitions over transversions, and frequent changes at the third codon position, in contrast with the gene evolution among more distant plant groups where biased nucleotide substitutions have frequently occurred. The sequences of these genes had diverged almost in proportion to taxonomic distance. The sequence of the pseudogene rpl23' changed approximately two times faster than that of the coding region. Sequence comparison between the pseudogene and its protein-coding counterpart revealed different degrees of nucleotide homology in wheat, rice and maize, suggesting that the transposition timing of the pseudogene differed and/or that different rates of gene conversion operated on the pseudogene in the cpDNA of the three plant groups in Gramineae. The intergenic spacer regions diverged approximately ten times faster than the genes. The divergence of wheat from barley, and that from rice are estimated based on the nucleotide similarity to be 1.5, 10 and 40 million years, respectively.     

Conserved sequences in both coding and 5'' flanking regions of mammalian opal suppressor tRNA genes.

The rabbit genome encodes an opal suppressor tRNA gene. The coding region is strictly conserved between the rabbit gene and the corresponding gene in the human genome. The rabbit opal suppressor gene contains the consensus sequence in the 3' internal control region but like the human and chicken genes, the rabbit 5' internal control region contains two additional nucleotides. The 5' flanking sequences of the rabbit and the human opal suppressor genes contain extensive regions of homology. A subset of these homologies is also present 5' to the chicken opal suppressor gene. Both the rabbit and the human genomes also encode a pseudogene. That of the rabbit lacks the 3' half of the coding region. Neither pseudogene has homologous regions to the 5' flanking regions of the genes. The presence of 5' homologies flanking only the transcribed genes and not the pseudogenes suggests that these regions may be regulatory control elements specifically involved in the expression of the eukaryotic opal suppressor gene. Moreover the strict conservation of coding sequences indicates functional importance for the opal suppressor tRNA genes.     

The keratin BIIIB gene family: isolation of cDNA clones and structure of a gene and a related pseudogene

The nucleotide sequence of cDNA clones encoding the three major BIIIB high-sulfur wool keratin proteins (BIIIB2, 3, and 4) and the structure of a BIIIB4 gene and a BIIIB3 pseudogene are reported. Although Southern blot analysis indicates that the BIIIB genes comprise a multigene family in the sheep genome, they are poorly represented in genomic DNA libraries. The family sequence homology of the coding region extends into the 5' and 3' untranslated regions and the near 5' flanking region of the BIIIB3 and 4 genes. These homologies suggest that the BIIIB3 and 4 genes represent the latest gene duplication event in the evolution of the BIIIB multigene family. Like the genes coding for other wool keratin matrix protein components, the BIIIB genes have the conserved 18-bp sequence immediately 5' to the initiation codon and also appear to lack introns.     

Comparison of the nucleotide sequences of a yeast gene family. I. Distribution and spectrum of spontaneous base substitutions

The nucleotide sequences of closely related members of a gene family can be used to investigate spontaneous mutations. Here we analyse the sequences of different yeast invertase genes which are more than 93% identical in the coding region and share some very similar, but not identical sequences in the noncoding flanking regions. Since all except one of the invertase genes are active, most of the base substitutions are silent. Within the coding region the base substitutions are unevenly distributed, indicating that parts of the genes were homogenized, probably via gene conversion. Transitions occurred more frequently than transversions in both, coding and noncoding regions. In the coding region pyrimidine transitions were the most abundant event due to silent changes mainly in the third codon position. In the noncoding region pyrimidine and purine transitions were found at equal frequencies. Transversions inverting base pairs (A-T and G-C) outnumber transversions changing base pairs (A-C and G-T). While the spectrum of mutations in the coding region is influenced by selective pressure to maintain the amino acid sequence, the spectrum in the noncoding region may be much less affected by selective pressure.     

Structural comparison of yeast ribosomal protein genes.

The primary structure of the genes encoding the yeast ribosomal proteins L17a and L25 was determined, as well as the positions of the 5'- and 3'-termini of the corresponding mRNAs. Comparison of the gene sequences to those obtained for various other yeast ribosomal protein genes revealed several similarities. In all split genes the intron is located near the 5'-side of the amino acid coding region. Among the introns a clear pattern of sequence conservation can be observed. In particular the intron-exon boundaries and a region close to the 3'-splice site show sequence homology. Conserved sequences were also found in the leader and trailer regions of the ribosomal protein mRNAs. The 5'-flanking regions of the yeast ribosomal protein genes appeared to contain sequence elements that many but not all ribosomal protein genes have in common, and therefore may be implicated in the coordinate expression of these genes. The amino acid coding sequences of the ribosomal protein genes show a biased codon usage. Like most yeast ribosomal protein molecules, L17a and L25 are particularly basic at their N-terminus.     

Linkage map of two HLA-SB beta and two HLA-SB alpha-related genes: an intron in one of the SB beta genes contains a processed pseudogene

Three overlapping cosmid clones contain coding sequences for four HLA Class II genes, provisionally identified as two HLA-SB alpha and two HLA-SB beta genes. The genes are in the order beta, alpha, beta, alpha, inverted with respect to each other. One of the SB beta genes contains a 513 bp sequence that appears to be a processed pseudogene, flanked by direct 17 bp repeat sequences, in the intron upstream of the beta 1 exon. The pseudogene is homologous to a family of sequences of approximately 25-40 members, most of which are not on chromosome 6. A cDNA clone, highly homologous to the pseudogene, except for its 5' end, contains a normal poly(A) addition site and a poly(A) tail. The cDNA clone is homologous to a single-copy gene in both man and mouse, encoded on human chromosome 15. A search of published DNA sequences identified a mouse sequence, with about 77% similarity to the pseudogene sequence, in the negative strand of an intron in a mouse dihydrofolate reductase gene. The second SB beta gene does not contain the pseudogene sequence.     

Organization of the human protein S genes

Human genomic clones that span the entire protein S expressed gene (PS alpha) and the 3' two-thirds of the protein S pseudogene (PS beta) have been isolated and characterized. The PS alpha gene is greater than 80 kilobases in length and contains 14 introns and 15 exons, as well as 6 repetitive "Alu" sequences. Exons I and XV contain 112 and 1139 bp 5' and 3' noncoding segments in addition to the amino and carboxyl termini, respectively. Exons I-VIII encode protein segments that are homologous to the vitamin K dependent clotting proteins and are bounded by introns whose position and type are identical with other members of this protein family. Exons IX-XV encode protein segments homologous to sex hormone binding globulin (SHBG) and are bounded by introns of identical type and position as in the SHBG gene. Genomic clones for the PS beta gene cover a distance of greater than 55 kilobases and contain segments corresponding to amino acids 46-635 of the mature protein and the 1.1-kb 3' noncoding region of the cDNA. The presence of multiple base changes in the coding portions of this gene, resulting in termination codons and frame shifts, suggests that it is a pseudogene. Comparison of DNA sequences for the two genes reveals 97% identity for coding and 3' noncoding, and 95.4% for intronic regions, suggesting divergence of the two genes is a relatively recent event.     

Inactivation of human keratin genes: the spectrum of mutations in the sequence of an acidic keratin pseudogene

Keratins are cytoskeletal proteins encoded by a multigene family. We have identified the first human keratin pseudogene and determined its complete nucleotide sequence. Sequence comparisons indicate that the pseudogene arose from a very recent duplication of the 50-kd keratin (K14) gene. The coding and the intron sequences of the two genes are 95% and 93% identical, respectively. Although the sequence of the regulatory region in the pseudogene is virtually identical to that in the 50-kd functional gene, several deleterious mutations have been identified in the pseudogene. There are three frameshifts in the coding regions, one of which is a perfect 8-bp duplication. A single-base-pair deletion in the first exon and a single-base-pair insertion in the penultimate exon also result in frameshifts. The three remaining deleterious mutations interfere with the mRNA processing signals: two alter the intron/exon boundaries, and the third disrupts the polyadenylation signal. These mutations clearly identify the sequence as a human keratin pseudogene.