RECIPROCAL INTERFERENCES BETWEEN NUCLEOSOMAL ORGANIZATION AND TRANSCRIPTIONAL ACTIVITY OF THE YEAST SNR6 GENE

Recent work has demonstrated a repressive effect of chromatin on the t ranscription of the yeast SNR6 gene in vitro. Here, we show the relati ons between chromatin structure and transcriptional activity of this g ene in vivo. Analysis of the SNR6 locus by micrococcal nuclease digest ion showed a protection of the TATA box, nuclease-sensitive sites arou nd the A and B blocks, and arrays of positioned nucleosomes in the fla nking regions. Analysis of a transcriptionally silent SNR6 mutant cont aining a 2-bp deletion in the B block showed a loss of TATA-protection and rearrangement or destabilization of nucleosomes in the flanking r egions. Hence, SNR6 organizes the chromatin structure in the whole reg ion in a manner dependent on its transcriptional state. Transcriptiona l analysis was performed by use of maxi-gene SNR6 constructs introduce d into histone-mutated strains. Chromatin disruption induced by histon e H4 depletion stimulated the transcription of promoter-deficient, but not of wild-type SNR6 genes, revealing a competition between the form ation of nucleosomes and the assembly of Pol III transcription complex es that was much in favor of transcription factors. On the other hand, amino-terminal mutations in histone H3 or H4 had no effect (H4) or on ly a moderate stimulatory effect (H3) on the transcription of promoter -deficient SNR6 genes.