Novel role for a Saccharomyces cerevisiae nucleoporin, nup170p, in chromosome segregation

We determined that a mutation in the nucleoporin gene NUP170 leads to defec ts in chromosome transmission fidelity (ctf) and kinetochore integrity in S accharomyces cerevisiae. A ctf mutant strain, termed s141, shows a transcri ption readthrough phenotype and stabilizes a dicentric chromosome fragment in two assays for kinetochore integrity. Previously, these assays led to th e identification of two essential kinetochore components, Ctf13p and Ctf14p . Thus, s141 represents another ctf mutant involved in the maintenance of k inetochore integrity. We cloned and mapped the gene complementing the ctf m utation of s141 and showed that it is identical to the S. cerevisiae NUP170 gene. A deletion strain of NUP170 (nup170 Delta::HIS3) has a Ctf(-) phenot ype similar to the s141 mutant (nup170-141) and also exhibits a kinetochore integrity defect. We identified a second nucleoporin, NUP157, a homolgue o f NUP170, as a suppressor of the Ctf(-) phenotype of nup170-141 and nup170 Delta::HIS3 strains. However, a deletion of NUP157 or several other nucleop orins did not affect chromosome segregation. Our data suggest that NUP170 e ncodes a specialized nucleoporin with a unique role in chromosome segregati on and possibly kinetochore function.