Abstract

SIT4 is the catalytic subunit of a type 2A-related protein phosphatase in Saccharomyces cerevisiae that is required for G1 cyclin transcription and for bud formation. SIT4 associates with several high-molecular-mass proteins in a cell cycle-dependent fashion. We purified two SIT4-associated proteins, SAP155 and SAP190, and cloned the corresponding genes. By sequence homology, we isolated two additional SAP genes, SAP185 and SAP4. Through such an association is not yet proven for SAP4, each of SAP155, SAP185, and SAP190 physically associates with SIT4 in separate complexes. The SAPs function positively with SIT4, and by several criteria, the loss of all four SAPs is equivalent to the loss of SIT4. The data suggest that the SAPs are not functional in the absence of SIT4 and likewise that SIT4 is not functional in the absence of the SAPs. The SAPs are hyperphoshorylated in cells lacking SIT4, raising the possibility that the SAPs are substrates of SIT4. By sequence similarity, the SAPs fall into two groups, the SAP4/SAP155 group and the SAP185/SAP190 group. Overexpression of a SAP from one group does not suppress the defects due to the loss of the other group. These findings and others indicate that the SAPs have distinct functions.

Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.