ROK1, A HIGH-COPY-NUMBER PLASMID SUPPRESSOR OF KEM1 ENCODES A PUTATIVE ATP-DEPENDENT RNA HELICASE IN SACCHAROMYCES-CEREVISIAE

The KEM1 gene is involved in nuclear fusion during conjugation, and ch romosome transmission and spindle pole body duplication/or separation during mitotic cell division in the yeast Saccharomyces cerevisiae. KE M1 was also independently identified as DST2, SEP1, XRN1 and RAR5 on t he basis of DNA strand transferase or exoribonuclease activity in vitr o or mutations affecting plasmid stability. To understand the various functions suggested for KEM1 and to identify other genes with function s similar or related to those of KEM1, we have characterized the ROK1 gene which was isolated as a high-copy-number plasmid suppressor of th e kem1 null mutation. Sequence analysis of the smallest subclone with the suppression activity revealed an open reading frame of 564 amino a cids. The ROK1 aa sequence contains highly conserved domains found in the DEAD protein family of ATP-dependent RNA helicases. ROK1 is essent ial for viability and is closely linked to KEM1 on chromosome VII.