Exon 1beta Research Articles

MSS18, a yeast nuclear gene involved in the splicing of intron aI5 beta of the mitochondrial cox1 transcript.

We have isolated and characterized a nuclear gene, MSS18, which is implicated in the splicing of intron aI5 beta of the mitochondrial cox1 transcript (subunit 1 of the cytochrome c oxidase). Northern blotting and S1 nuclease protection experiments as well as the analysis of mitochondrial point revertants suggest that mss18 mutations block (perhaps indirectly) the cleavage of the 5' exon-intron junction of aI5 beta. Mitochondrial point revertants also indicate that up to 13 bases of the aI5 beta exon sequence, upstream of the 5' splice site of aI5 beta, are involved in vivo in the splicing of this intron. The implications of this result on the splicing of group I introns are discussed.

Genomic DNA encoding rabbit T cell receptor beta-chains: isotypes and allotypes of C beta.

We have discovered sequence differences in DNA encoding the first exon of rabbit T cell receptor beta-chains from unrelated rabbits that probably reflect allelic C beta 1 allotypes. Rabbit I was from a colony bred to maintain the K1-expression mutation Basilea, and rabbit II was from a colony bred to maintain the K1b9 allotype. Genomic DNA from rabbits I and II also exhibit restriction fragment length polymorphism of C beta on Southern blots. In addition, several different restriction enzyme digests of DNA from rabbit I give three bands, whereas DNA from rabbit II gives two when probed with C beta. An approximately 14-kb cloned genomic DNA fragment from rabbit I has two copies of C beta exon 1 and a 6-kb fragment has a third copy, suggesting that rabbit I has three different C beta genes. The DNA sequence of a germ-line genomic DNA fragment encoding the first exon of the beta-chain constant region from rabbit I also has an open reading frame encoding 140 amino acids immediately 5' of the C beta sequence. A corresponding sequence had previously been found in a cDNA clone from the second rabbit (rabbit II).

"Exon-shuffling" maps control of antibody- and T-cell-recognition sites to the NH2-terminal domain of the class II major histocompatibility polypeptide A beta.

To investigate the role of the highly polymorphic amino-terminal (beta 1) domain of the class II major histocompatibility polypeptide A beta during recognition by T cells and antibodies, "exon-shuffling" was carried out between genomic recombinant DNA clones of Ak beta and Ad beta to generate a hybrid gene containing Ak beta exons for the amino-terminal domain followed by the Ad beta exons for the remainder of the molecule. L-cell gene transfectants expressing this hybrid A beta gene in combination with Ak alpha were compared to L cells expressing wild-type Ak beta Ak alpha dimers in tests of antigen-presentation to T-cell clones and hybridomas and for staining by a panel of anti-I-Ak-specific monoclonal antibodies. These antibodies were also tested for their reactivity with a B-lymphoma transfectant expressing Ak beta in the absence of Ak alpha. The results showed no qualitative differences in either T-cell or antibody-mediated recognition of I-Ak molecules containing either the exon-shuffled or wildtype Ak beta. Together with the data involving the B cell transfectant expressing only Ak beta, these results map control of the A beta contribution to the immunologically relevant determinants of I-Ak to the highly polymorphic amino-terminal domain and indicate little, if any, contribution to allele-specific recognition by amino acid sequence variations in the remaining portions of the A beta polypeptide.