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B Séraphin

Publications and source records attributed to B Séraphin.

64 records · Page 4Linked to original sources
PubMed1990

Exon mutations uncouple 5' splice site selection from U1 snRNA pairing.

It has previously been shown that a mutation of yeast 5' splice junctions at position 5 (GUAUGU) causes aberrant pre-mRNA cleavages near the correct 5' splice site. We show here that the addition of exon mutations to an aberrant cleavage site region transforms it into a functional 5' splice site both in vivo and in vitro. The aberrant mRNAs are translated in vivo. The results suggest that the highly conserved G at the 5' end of introns is necessary for the second step of splicing. Further analyses indicate that the location of the U1 snRNA-pre-mRNA pairing is not affected by the exon mutations and that the precise 5' splice site is selected independent of this pairing.

Base Sequence↗
PubMed1989

Mutational analysis of the interactions between U1 small nuclear RNA and pre-mRNA of yeast.

In recent experiments we have used the power of yeast genetics to study U1 small nuclear RNA (snRNA): pre-messenger RNA (pre-mRNA) base pairing interactions [Séraphin et al. EMBO J. 7 (1988) 2533-2538]. Here we extend these observations to other potential U1 snRNA: pre-mRNA pairings. We show that several U1 snRNA mutants are viable. Using these U1 mutant strains we demonstrate further a base-pairing interaction between U1 snRNA position 3 and intron position 6. However, this interaction is only detected with a poor splicing substrate containing branchpoint mutations. These results provide information on the mechanism of 5' splice site-branch point interaction. We also propose several models which may explain why the sequence of the 5' end of the U1 snRNA is conserved among organisms as divergent as man and yeast.

Animals↗
PubMed1989

Mitochondrial splicing requires a protein from a novel helicase family.

Proteins involved in mitochondrial splicing but encoded by nuclear genes have been characterized in Saccharomyces and Neurospora. The role in splicing of these proteins is largely unknown. Here we report that mutations in the nuclear gene MSS116 directly affect the splicing of several introns of the cytochrome b (cob) and cytochrome c oxidase subunit I (cox1) primary transcripts. This implies that the MSS116 protein (pMSS116) is an important component of the mitochondrial splicing machinery. The sequence of the cloned MSS116 gene shows that its protein product is homologous to the translation eIF-4A factor and the human nuclear protein p68. We show further that these proteins share several conserved amino-acid blocks with DNA helicases and related proteins. This suggests that pMSS116 has an RNA helicase activity. RNA helicases may be involved in many different processes including translation and splicing.

Amino Acid Sequence↗
PubMed1989

Mitochondrial introns aI1 and/or aI2 are needed for the in vivo deletion of intervening sequences.

Some pet- (or mit-) mutations impeding the splicing of one or several intron(s) of the yeast mitochondrial pre-mRNA(s) are suppressed in vivo by the DNA deletion of these introns. We have genetically demonstrated that introns aI1 and/or aI2 of the cytochrome c oxidase subunit 1 gene are necessary for this deletion process. The facts that adjacent introns are simultaneously deleted and that, in the pet- (or mit-) mutants which easily revert by intron deletion, the splicing of the introns they affect is only partially blocked, suggest that the intron encoded proteins aI1 and/or aI2 could intervene by means of their putative reverse transcriptase activity.

Chromosome Deletion↗
PubMed1988

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.

Amino Acid Sequence↗
PubMed1988

A U1 snRNA:pre-mRNA base pairing interaction is required early in yeast spliceosome assembly but does not uniquely define the 5' cleavage site.

We analyzed the effects of suppressor mutations in the U1 snRNA (SNR19) gene from Saccharomyces cerevisiae on the splicing of mutant pre-mRNA substrates. The results indicate that pairing between U1 snRNA and the highly conserved position 5 (GTATGT) of the intron occurs early in spliceosome assembly in vitro. This pairing is important for efficient splicing both in vitro and in vivo. However, pairing at position 5 does not appear to influence 5' splice site selection in vivo, indicating that the previously described U1 snRNA:5' splice junction base pairing interaction is not sufficient to define the 5' cleavage site.

Introns↗
PubMed1987

The mitochondrial reading frame RF3 is a functional gene in Saccharomyces uvarum.

The yeast mitochondrial genome contains three reading frames, RF1, RF2, and RF3, which are related to the group I maturases, though they are not intronic sequences. In the Saccharomyces cerevisiae strain D273-10B/A, these reading frames are interrupted by G + C-rich sequences (GC clusters) which break the frames. In the present work we described a Saccharomyces uvarum strain which possesses a RF3 continuous sequence devoid of GC clusters. Moreover, our results strongly suggest that in the same strain RF2 and RF1 are also continuous sequences. As all three RFs belong to transcription units which are highly expressed, it is most reasonable to assume that RF1, RF2, and RF3 are functional genes. Furthermore, we have discovered a rule which seems to explain the transposition of GC clusters, considered as mobile elements, in the mitochondrial genome.

Base Sequence↗
PubMed1987

Construction of a yeast strain devoid of mitochondrial introns and its use to screen nuclear genes involved in mitochondrial splicing.

We have constructed a respiring yeast strain devoid of mitochondrial introns to screen nuclear pet- mutants for those that play a direct role in mitochondrial intron excision. Intron-less mitochondria are introduced by cytoduction into pet- strains that have been made rho0; cytoductants therefrom recover respiratory competency if the original pet- mutation is required only for mitochondrial splicing. By this means, we have identified 11 complementation groups of such genes. Their total number may be estimated as about 18.

Cell Nucleus↗
PubMed1985

A mitochondrial reading frame which may code for a maturase-like protein in Saccharomyces cerevisiae.

In S. cerevisiae, the large oxi3/oli2 mitochondrial transcript contains the products of the oxi3, aap1 and oli2 genes and an unassigned reading frame, RF3. In the work presented here, we have completed the nucleotide sequence of RF3. We have shown that RF3 is composed of four fairly large ORFs which overlap within GC rich sequences. Furthermore, a shift of +1 base was found between each pair of consecutive reading frames. We discuss how these frameshifts could be removed to produce a 500 aminoacid long protein containing the two well conserved P1 and P2 oligopeptide sequences featuring several mitochondrial intron reading frames, suggesting, thereby, a RNA-maturase-like activity for the putative RF3 protein. In addition, we suggest that the insertion of GC clusters in a gene could provide a novel way of regulating its expression.

Base Sequence↗