G1 shortening following unbalanced growth: a specific v. nonspecific effect.
The synthesis and abundance of proteins were examined in synchronous populations of HeLa cells under conditions in which the lengthening of S phase, by inhibiting DNA synthesis, resulted in shortening of G1 in the subsequent generation. Mitotically collected cells were resynchronized by incubation with 3 microM aphidicolin from 3 to 12 h after mitotic selection; they were blocked again at various times thereafter to induce unbalanced growth. Cells were labelled with [35S]-methionine before and after release from the block to study the changes in protein synthesis. Triton X-100 soluble and insoluble proteins were analysed by 7-15% gradient SDS-PAGE, and radioactivity incorporation was quantified by liquid-scintillation counting. The degree of G1 shortening correlated with S phase position, increasing gradually from early S and reaching maximum when cells were blocked half-way through S phase. Synthesis of proteins of 120, 66, and 51 kDa was stimulated, and synthesis of a new protein of 57kDa was observed, in cells in which DNA synthesis had been blocked in mid-S. These proteins also showed increased accumulation. These results suggest that the shortening of G1, induced by the prior arrest of cell-cycle progression, is associated with synthesis of specific proteins rather than the non-specific accumulation of cellular proteins through unbalanced growth.
Goswami
P C
PC
Section of Cancer Biology, Washington University Medical Center, St. Louis, MO 63108.
Higashikubo
R
R
Tolmach
L J
LJ
Roti Roti
J L
JL
D016590:Aphidicolin / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D005434:Flow Cytometry; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D011506:Proteins / Q000378:metabolism*
D006657:Histones; D011506:Proteins; D016590:Aphidicolin