Developmentally regulated phosphoproteins associated with chromosome complexes in yeast

Previous studies on our laboratory have shown that nuclear DNA from Saccharomyces cerevisiae can be isolated in the form of fast-sedimenting chromosome complexes (FSCC). In cycling cells, three FSCC forms, denoted g1 and g2, can be distinguished by their characteristic sedimentation velocities and are found correspondingly in cells in G1, S and G2 of the cell cycle, respectively. A fourth form, denoted go, is found exclusively in stationary-phase and nitrogen-starved cells and defines the non-cycling state, Go. We used the differing sedimentation velocities of the FSCC of proliferating and non-cycling cells as a way to isolate and examine their associated proteins. We report here a two-dimensional polyacrylamide gel electrophoresis analysis of [35S]methionine and 32PO4-labelled proteins extracted from FSCC isolated from cycling cells (g1, r and g2, collectively denoted 'cycling FSCC'), and nutritionally arrested cells (go FSCC). Among the 120 35S-labelled FSCC-associated polypeptides detected, 25 were unique to go FSCC and 7 were unique to cycling FSCC. Among the 84 32P-labelled FSCC-associated polypeptides detected, 52 were unique to go FSCC and 7 were unique to cycling FSCC. Comigrating 35S and 32P-labelled polypeptides were matched in 34 of the 84 phosphorylated polypeptides, and 21 of these showed the same specificity of association to either cycling or go FSCC. This analysis demonstrates that there are major differences in the proteins associated with FSCC from cycling and nutritionally arrested cells, and indicates that a relationship exists between the growth state of the yeast cell, protein phosphorylation and chromosome-complex structure.