ARTIFICIAL ANTISENSE RNA REGULATION OF YBR1012 (YBR136W), AN ESSENTIAL GENE FROM SACCHAROMYCES-CEREVISIAE WHICH IS IMPORTANT FOR PROGRESSION THROUGH G1 S/

YBR1012 (YBR136w) is an essential gene from Saccharomyces cerevisiae i dentified during the systematic sequencing of part of the right arm of chromosome II. We previously constructed a conditional allele of YBR1 012 based on antisense RNA, by inserting a small fragment of this gene downstream from the inducible UASGAL10-CYC1 promoter. Several other a ntisense RNA constructions have since been made and their activity tes ted. The response of the system appears to be very delicate, as the pr esence or absence of 13 nucleotides of polylinker in the 300 nucleotid e antisense transcript can dramatically modify its effectiveness, The most effective antisense RNA construction was used in flow cytometry s tudies to investigate the role of ybr1012p. The results show that duri ng the antisense RNA block some 80% of the cells are arrested with the ir DNA unreplicated, suggesting that Ybr1012p is needed for progressio n through G1 or early S phase.