The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined. This is the first complete sequence analysis of an entire chromosome from any organism. The 315-kilobase sequence reveals 182 open reading frames for proteins longer than 100 amino acids, of which 37 correspond to known genes and 29 more show some similarity to sequences in databases. Of 55 new open reading frames analysed by gene disruption, three are essential genes; of 42 non-essential genes that were tested, 14 show some discernible effect on phenotype and the remaining 28 have no overt function.

We have dissected the mouse H-2Kb gene promoter in order to define the sequences responsible for induction by tumour necrosis factor (TNF-az). An enhancer element (-187 to -158) composed of two imperfect direct palindromic repeats has been shown to be necessary and sufficient for TNF-a induction of a heterologous promoter. A multimer of either repeat is also responsive, while a single copy is not: this is the situation in the ,B2-microglobulin (j2-m) promoter which contains a single palindrome and does not respond to TNF-a. We had previously found that the two repeats can bind a factor named KBF1. We show here that in the uninduced state the transcription factor AP2 binds to the interpalindromic region, while in TNF-treated cells an NFxB-like activity is induced which displaces both KBF1 and AP2 and binds to the two palindromes. This strongly suggests that induction of an NFxB-like activity is responsible for TNF-ca stimulation of mouse MHC class I genes.

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The MSS51 gene product has been previously shown to be involved in the splicing of the mitochondrial pre-mRNA of cytochrome oxidase subunit I (COX1). We show here that it is specifically required for the translation of the COX1 mRNA. Furthermore, the paromocyin-resistance mutation (P454R) which affects the 15S mitoribosomal RNA, interferes, directly or indirectly, with the action of the MSS51 gene product. Possible roles of the MSS51 protein on the excision of COX1 introns are discussed.

Human interferons‐alpha, ‐beta and ‐gamma enhance HLA‐DR mRNAs in all the human lymphoblastoid and melanoma cell lines studied. The increase concerns both alpha and beta chain mRNAs. Moreover, we show that immune interferon‐gamma preferentially enhances class II MHC mRNA. This effect of IFN‐gamma on the synthesis of alpha and beta HLA‐DR chains has been also analysed by immunoprecipitation. It is abolished by a monoclonal antibody directed against human IFN‐gamma. The effect of interferon on the cell surface level of HLA‐DR molecules does not always correspond to the enhancement of HLA‐DR mRNA. Our experiments suggest that this discrepancy between the enhancement of HLA‐DR mRNA and cell surface antigen might be due to a constitutively high level of the corresponding antigens on several of the human cells studied.

Using a Y specific probe (pY353/B) taken from a flow sorted mouse Y chromosome library we have identified a family of RNA transcripts encoded by the Y chromosome. These transcripts which are approximately 1.3 Kb in length are present in testis PolyA+ RNA but can not be detected in either male liver, spleen, kidney, brain, heart or lung tissues. Isolation and sequence analysis of a corresponding cDNA shows it to contain a potential coding sequence of 696bp. These data show that the Y chromosome is transcriptionally active in the adult mouse testis.

The pal 4 nuclease (termed I-Sce II) is encoded in the group I al 4 intron of the COX I gene of Saccharomyces cerevisiae. It introduces a specific double-strand break at the junction of the two exons A4-A5 and thus mediates the insertion of the intron into an intronless strain. To define the sequence recognized by pal 4 we introduced 35 single mutations in its target sequence and examined their cleavage properties either in vivo in E. coli (when different forms of the pal 4 proteins were artificially produced) or in vitro with mitochondrial extracts of a mutant yeast strain blocked in the splicing of the al 4 intron. We also detected the pal 4 DNA endonuclease activity in extracts of the wild type strain. The results suggest that 6 to 9 noncontiguous bases in the 17 base-pair region examined are necessary for pal 4 nuclease to bind and cleave its recognition site. We observed that the pal 4 nuclease specificity can be significantly different with the different forms of the protein thus explaining why only some forms are highly toxic in E. coli. This study shows that pal 4 recognition site is a complex phenomenon and this might have evolutionary implications on the transfer properties of the intron.

To purify mouse Y chromosomes by flow cytometry, a male cell line containing the Robertsonian translocation Rb(9.19)163H has been established by SV40 transformation. Flow karyotypes obtained from these cells exhibit a well-isolated peak of fluorescence corresponding to the single Y chromosome, clearly distinct from that of chromosome 19. From this peak, 650,000 chromosomes were sorted, and two restriction fragment libraries were constructed from the DNA of the sorted chromosomes. The characterization of several Y-specific fragments has shown that the Y DNA was enriched at least 36-fold. Furthermore, given that there are likely homologies between the X and Y chromosomes, we can assume that this calculated value of the purification factor is an underestimation and that the Y DNA was more highly purified by flow sorting.