No abstract

RNA polymerases frequently deal with a number of obstacles during transcription elongation that need to be removed for transcription resumption. One important type of hindrance consists of DNA lesions, which are removed by transcription-coupled repair (TC-NER), a specific sub-pathway of nucleotide excision repair. To improve our knowledge of transcription elongation and its coupling to TC-NER, we used the yeast library of non-essential knock-out mutations to screen for genes conferring resistance to the transcription-elongation inhibitor mycophenolic acid and the DNA-damaging agent 4-nitroquinoline-N-oxide. Our data provide evidence that subunits of the SAGA and Ccr4-Not complexes, Mediator, Bre1, Bur2, and Fun12 affect transcription elongation to different extents. Given the dependency of TC-NER on RNA Polymerase II transcription and the fact that the few proteins known to be involved in TC-NER are related to transcription, we performed an in-depth TC-NER analysis of a selection of mutants. We found that mutants of the PAF and Ccr4-Not complexes are impaired in TC-NER. This study provides evidence that PAF and Ccr4-Not are required for efficient TC-NER in yeast, unraveling a novel function for these transcription complexes and opening new perspectives for the understanding of TC-NER and its functional interconnection with transcription elongation.

Genes encoding elements of four amino acid permeases were identified by insertional inactivation of ORFs from the genomic sequence of the cyanobacterium Synechocystis sp. strain PCC 6803 whose putative products are homologous to amino acid permease proteins from other bacteria. A transport system for neutral amino acids and histidine and a transport system for basic amino acids and glutamine were identified as ABC-type transporters, whereas Na + -dependent transport of glutamate was found to be mediated by at least two systems, the secondary permease GltS and a TRAP-type transporter. Except for GltS, substrate specificities of the identified permeases do not match those of previously characterized systems homologous to these permeases.