Developmentally regulated phosphoproteins associated with chromosome complexes in yeast

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Nuclear DNA in Saccharomyces cerevisiae can be isolated as fast-sedimenting chromosome complexes (FSCC).
• Three FSCC forms (g1, r, g2) exist in cycling cells (G1, S, G2 phases), and a fourth (go) in non-cycling, stationary-phase cells.
• Sedimentation velocities differ between proliferating and non-cycling cell FSCC.

Purpose of the Study:

• To isolate and examine proteins associated with FSCC from cycling and non-cycling yeast cells.
• To investigate differences in protein composition and phosphorylation states between FSCC forms.
• To explore the relationship between yeast cell growth state, protein phosphorylation, and chromosome-complex structure.

Main Methods:

• Isolation of fast-sedimenting chromosome complexes (FSCC) from cycling and nutritionally arrested Saccharomyces cerevisiae.
• Two-dimensional polyacrylamide gel electrophoresis analysis of [35S]methionine and 32PO4-labelled proteins.
• Comparative analysis of protein profiles and phosphorylation patterns between different FSCC forms.

Main Results:

• Significant differences in associated polypeptides were found between cycling (g1, r, g2) and non-cycling (go) FSCC.
• 25 [35S]-labelled and 52 32P-labelled polypeptides were unique to go FSCC, while 7 of each were unique to cycling FSCC.
• 34 phosphorylated polypeptides were matched, with 21 showing specific association to either cycling or go FSCC.

Conclusions:

• Major differences exist in proteins associated with FSCC from cycling versus arrested yeast cells.
• Protein phosphorylation patterns vary significantly between FSCC from different growth states.
• A relationship is indicated between yeast cell growth state, protein phosphorylation, and the structure of chromosome complexes.