Coordination of daughter cell growth and nuclear division are readily observed but not well understood in the yeast Saccharomyces cerevisiae . A screen was performed to identify mutants which lost this coordination such that they exhibited an elongated cell morphology (improper cell growth), but continued to divide. The results of this screen and suppressor analysis suggests the bud neck ring is a control structure which determines cell morphology as well as nuclear division as an upstream regulator of Cdc28p-cyclin complexes.;The effects of mutations in specific components of the bud neck ring on the assembly of other components into the structure are examined. First, molecular characterization of the mutations was undertaken. The original elm1-1 allele results in replacement of Thr-311 by an isoleucine. The original elm2-1 allele contains a nonsense mutation in codon 790. The original elm13-1 allele of the gene CDC12 causes replacement of Arg-363 by a lysine. Finally, the Sel2-1 allele of the ELM2/HSL1 gene, which supresses elm1-1, causes replacement of Met-177 by a valine. Next, assembly interdependence of these three proteins was determined. Localization interdependence between Elm1p, Elm2/Hs11p, and Cdc12p in regard to correct initial as well as proper sustained localization to the neck ring was found. A mutation in CDC28 which results in constitutive elongated cell morphology was found to have a negligible effect on localization of bud neck ring proteins. These results support the bud neck ring as an upstream effector of Cdc28p-cyclin complexes.;In an attempt to better understand the involvement of Elm1p in control the G2/M transition, a search for proteins interacting with Elm1p was undertaken. Elm1p was precipitated from yeast cells and interacting proteins were identified through probing with proteins specific antibodies. Through these co-purification experiments, a specific interaction was found between Elm1p, Gin4p Nap1p and Clb2p. These associations were specific and reproducible. Gene disruptions and C-terminal truncations of Elm1p were also used to identify the order of these interactions. This new data suggests that Elm1p may have a more direct role in control of Cdc28p-Clb2p complexes than previously determined.