The CCG1 cDNA encoding a general transcription factor, TAFII250, complements a thermosensitive (ts) cell cycle mutant, tsBN462, of the BHK21 cell line, which arrests in the G1 phase at the restrictive temperature. In order to clarify whether the CCG1 is mutated in tsBN462 cells or a suppressor of tsBN462 mutation, CCG1 cDNAs isolated from parental wild-type (wt) BHK21 and tsBN462 cell lines were sequenced. Comparison of the nucleotide (nt) sequences showed a single transition: G→A in the second base of codon 690 of the tsBN462 CCG1 cDNA, resulting in a Gly290→Asp change. The BHK CCG1 cDNA, but not the tsBN462 CCG1 cDNA, complemented the tsBN462 mutation, proving that the CCG1 is mutated in the tsBN462 cell line. Thus, the defect of general transcription factor, TAFII250, is suggested to cause a G1 arrest in the cell cycle.
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