A single nucleotide difference at the 3'' end of an intron causes differential splicing of two histocompatibility genes.

The murine histocompatibility class I genes, H-2 Kb and Kk, display considerable homology at their 3' ends. In fact, from exon 5 to the termination codon, only two nucleotides differ between the two genes, one at the 5' end and the other at the 3' end of intron 7. Despite this similarity, the gene products have distinctly different mol. wts as determined by SDS-PAGE. By constructing two hybrid genes, pC2 and pC4, we demonstrated that it is the cytoplasmic parts of the antigens (encoded by exons 6-8) which are responsible for the major difference in mol. wt. We have used site-directed mutagenesis to change the two nucleotides in intron 7 of the H-2 Kk gene to those present in the H-2 Kb gene. S1 nuclease mapping has been used to identify the actual splice site of the authentic Kb and Kk genes, the hybrid genes and the mutagenized genes. We have shown that it is the 3' nucleotide difference, nine nucleotides upstream of the 3' splice site, which causes the different excision of intron 7 of the Kb gene. The 5' nucleotide difference does not alter the splicing. The choice of branch points and 3' splice signals for intron 7 of five H-2 class I genes, is discussed.     

A gene required for RNase P activity in Candida (Torulopsis) glabrata mitochondria codes for a 227-nucleotide RNA with homology to bacterial RNase P RNA.

We have mapped a gene in the mitochondrial DNA of Candida (Torulopsis) glabrata and shown that it is required for 5' end maturation of mitochondrial tRNAs. It is located between the tRNAfMet and tRNAPro genes, the same tRNA genes that flank the mitochondrial RNase P RNA gene in the yeast Saccharomyces cerevisiae. The gene is extremely AT rich and codes for AU-rich RNAs that display some sequence homology with the mitochondrial RNase P RNA from S. cerevisiae, including two regions of striking sequence homology between the mitochondrial RNAs and the bacterial RNase P RNAs. RNase P activity that is sensitive to micrococcal nuclease has been detected in mitochondrial extracts of C. glabrata. An RNA of 227 nucleotides that is one of the RNAs encoded by the gene that we mapped cofractionated with this mitochondrial RNase P activity on glycerol gradients. The nuclease sensitivity of the activity, the cofractionation of the RNA with activity, and the homology of the RNA with known RNase P RNAs lead us to propose that the 227-nucleotide RNA is the RNA subunit of the C. glabrata mitochondrial RNase P enzyme.     

Cloning and characterization of a linear 2.3 kb mitochondrial plasmid of maize

Summary A linear 2.3 kb DNA molecule found in maize mitochondria was cloned into pUC8. A natural deletion of this plasmid, found in cmsT and some N (fertile) types of maize plants, was mapped to one end of the plasmid. A minor sequence homology to S-2, another linear mitochondrial plasmid, was detected, as well as more significant sequence homology with chloroplast and maize nuclear DNA. Hybridization to teosinte mitochondrial DNA (mtDNA) revealed the presence of part of the maize plasmid in the high molecular weight mtDNA of the maize relatives. RNA dot hybridization indicates that the plasmid is transcribed in mitochondria. The termini of the 2.3 kb linear plasmid contain inverted repeated sequences; of the first 17 nucleotides of the termini, 16 are identical to the terminal inverted repeats of the linear S plasmids found in the mitochondria of cmsS maize plants.     

Nucleotide sequence of the genes III, VI and I of bacteriophage M13.

A DNA region of 2750 base pairs encompassing the genes III, VI and I of bacteriophage M13 has been sequenced by the Maxam-Gilbert procedure. By establishing the nucleotide changes introduced by several amber mutations, the coding region and the regulatory signals of each gene have been deduced. The genes appear to span 1275 base pairs (gene III; mol.wt. 44,748) 339 base pairs (gene VI; mol.wt. 12,264) and 1047 base pairs (gene I; mol.wt. 39,500). Their separating non-codogenic regions are extremely short, namely two and one base pair, respectively. The C-terminal end of gene I, however, intrudes 23 nucleotides into gene IV. From the nucleotide sequence it appears that the minor capsid protein of the phage, which is encoded by gene III, is synthesized in a precursor form containing 18 extra amino acids at its N-terminal end. Furthermore, in this capsid protein two clusters of a fourfold repeat of the sequence Glu-Gly-Gly-Gly-Ser are apparent. Gene VI appears to code for a small, extremely hydrophobic polypeptide. Its total hydrophobic amino acids content of 51% suggests that this protein can only function in the host cell membrane.     

Terminal protein association and sequence homology in linear mitochondrial plasmid-like DNAs of sorghum and maize

The linear extrachromosomal mitochondrial plasmid-like DNAs from the Ru cytoplasm of maize, and M35-1 and IS1112C cytoplasms of sorghum, possess 5 terminally-attached proteins. These molecules required proteinase K treatment for mobility in agarose gels and were susceptible to exonuclease III but not lambda exonuclease cleavage. Hybridizations, under stringent conditions, indicated that the sorghum plasmid-like DNAs, N1 and N2, did not possess DNA sequence homology to cloned central regions of S1 and S2, the linear mitochondrial plasmid-like DNAs present in S cytoplasm of maize. In addition, a novel 4.2kb, DNAase sensitive, RNAase insensitive band, exhibiting homology to internal sequences from maize S2, was observed in the sorghum IS1112C cytoplasm only.     

Nucleotide sequence encoding the 5'' end of Xenopus laevis 18S rRNA.

We have sequenced a region of cloned Xenopus laevis ribosomal DNA encompassing the last 24 nucleotides of the external transcribed spacer and the first 275 nucleotides of the 18S gene. The start of the 18S gene was identified by correlating the results obtained from RNA hybridization and fingerprinting with the DNA sequence. This 5' region of 18S rRNA contains five 2'-O-methyl groups and at least six pseudouridine residues. Several of these modified nucleotides are clustered into a relatively short region from nucleotides 99-124. Nucleotides 227-250 constitute a distinctive sequence of 24 consecutive G and C residues. Comparison with the first 160 nucleotides of a yeast 18S gene (25) reveals three blocks of high sequence homology separated by two short tracts where homology is low or absent. The external transcribed spacer sequences diverge widely from within a few nucleotides of the start of the 18S gene.     

Nucleotide sequence and structural organization of the 3'-terminal region of potato virus M

The sequence of 2630 3'-terminal nucleotides has been determined for the genomic RNA of potato virus M (PVM), a type member of the carlavirus group. Analysis of this nucleotide sequence revealed five open reading frames coding for proteins of mol. wt. 25, 12, 7, 34 and 11 kDa (in 5'----3' direction). The PVM genome organization has been shown to be basically analogous to that of potexviruses, except that the latter at their 3' end lack the gene encoding 11K protein. Amino acid sequence comparison between the PVM 34K protein and the coat proteins of potexviruses has shown a high extent of homology in the C-terminal amino acids. Homology has also been found between the 25, 12 and 7K proteins encoded by PVM RNA and corresponding potexvirus proteins. All this gave grounds for suggestion that carlaviruses and potexviruses belong to the same subgroup of phytoviruses.