Plo1p may function early in the pathway since its overexpression can induce septum formation in interphase, suggesting that Plo1p drives both actin ring formation and activation of the sid pathway (Ohkura is unknown; however, since Sid2p seems to function immediately downstream of Sid1pCCdc14p, one model is usually that Sid2p or an associated protein could be substrates for Sid1p
Plo1p may function early in the pathway since its overexpression can induce septum formation in interphase, suggesting that Plo1p drives both actin ring formation and activation of the sid pathway (Ohkura is unknown; however, since Sid2p seems to function immediately downstream of Sid1pCCdc14p, one model is usually that Sid2p or an associated protein could be substrates for Sid1p. al., 1995). Under restrictive conditions, cells bearing temperature-sensitive alleles of the genes show normal medial ring assembly and redistribution of actin patches, but fail to initiate ring constriction and septum deposition. These cells proceed through additional nuclear division cycles without septation, becoming long and multinucleate before eventually lysing (Fankhauser et al., 1995; Balasubramanian et al., 1998). Plo1p seems to play a role in cytokinesis since it is required for septum formation and its overexpression in interphase results in Nedaplatin septum formation (Ohkura et al., 1995). Genetic and biochemical studies suggest that the gene products function in a novel signaling cascade regulating cytokinesis, yet their order of function is usually unclear (Marks et al., 1992; Balasubramanian et al., 1998; Sohrmann et al., 1998). Based on localization studies, at least part of this cascade appears to function by transducing septum-promoting signals from spindle pole body (SPBs) to the division site. Spg1p, a small GTPase of the ras superfamily, Nedaplatin localizes to SPBs throughout interphase in an active GDP-bound form. Upon access into mitosis, Spg1p is usually converted to an active GTP-bound state until anaphase, when conversion of Spg1pCGTP to Spg1pCGDP occurs at one SPB (Sohrmann et Nedaplatin al., 1998). Bry4p and Cdc16p function together as the GTPase-activating protein (Space) for Spg1p (Furge et al., 1998); however, Nedaplatin the GDP/GTP exchange factor (GEF) has not yet been recognized. Moreover, Byr4p/Cdc16p co-localizes with Spg1pCGDP but not Spg1pCGTP (Cerutti and Simanis, 1999). The key RGS21 function of Spg1pCGTP appears to be in localizing Cdc7p kinase to the SPB during mitosis since Cdc7p kinase activity does not seem to be regulated (Sohrmann et al., 1998). Sid2p kinase is usually localized to the single SPB in interphase, both SPBs during mitosis and transiently to the cleavage site during medial ring constriction and septation. Sid2p kinase activity peaks during late anaphase and its Nedaplatin localization and kinase activity require the other genes, suggesting that it functions late in the cascade (Sparks et al., 1999). Cdc14p has been cloned but does not display significant sequence similarity to any known proteins (Fankhauser and Simanis, 1993). Overproduction of Cdc14p results in a G2CM block; however, Cdc14p localization and where it functions in the sid pathway have not been described. In this study, we investigated the role of Sid1p and Cdc14p in the sid pathway. We show that Sid1p is usually a PAK/GC family protein kinase that functions in a complex with Cdc14p, downstream of Spg1pCCdc7p and upstream of Sid2p. We also show that Sid1p localization may be regulated by Cdc2Ccyclin activity, suggesting a mechanism that may couple cytokinesis with completion of mitosis. Results Cloning and disruption of sid1 The gene was cloned by complementation of a temperature-sensitive mutant. corresponded to an open reading frame with GenBank accession No. “type”:”entrez-protein”,”attrs”:”text”:”CAB11493″,”term_id”:”2370557″CAB11493. encodes a 471 amino acid protein kinase of the PAK/GC kinase family (for a review, see Sells and Chernoff, 1997). A sequence comparison of the catalytic domain name of Sid1p and catalytic domains from related proteins is usually shown in Physique?1A. Sid1p is usually most related to GC kinases that have an N-terminal kinase domain name and a C-terminal half with little homology to known proteins. A null allele of was constructed using a one-step gene replacement strategy in a diploid strain, and was found to be essential for viability (observe Materials and methods). null cells become long and multinucleate, identical to the phenotype of cells with temperature-sensitive alleles at restrictive heat (data not shown). Open in a separate windows Fig. 1. Kinase activity is essential. (A)?Alignment of the catalytic domain name of Sid1p with the catalytic domains of the most closely related PAK/GC family members as determined by the BLAST and MULTALIN programs. Relatives include severin kinase from (“type”:”entrez-protein”,”attrs”:”text”:”AAC24522″,”term_id”:”3075511″AAC24522), contig yk19h11.5 (AAC9038), BnMAPK4 from (“type”:”entrez-protein”,”attrs”:”text”:”CAA08757″,”term_id”:”3819697″CAA08757), human Ste20-like kinase Mst-3 (4505261) and human oxidant stress-activated Ste20-like kinase SOK-1 (5454174). Roman numerals indicate the 11 subdomains characteristic ofSer/Thr protein.