SEQUENCE AND EXPRESSION IN ESCHERICHIA-COLI OF THE 40-KDA SUBUNIT OF ACTIVATOR-1 (REPLICATION FACTOR-C) OF HELA-CELLS

Activator 1 (A1; also called replication factor C), in conjunction wit h proliferating-cell nuclear antigen (PCNA), is essential for the elon gation of primed DNA templates by DNA polymerases-delta and epsilon. A 1 contains five distinct subunits of 145, 40, 38, 37, and 36.5 kDa. He re we describe the isolation, sequence, and bacterial expression of a cDNA coding for the 40-kDa subunit. In keeping with the presence of an ATP-binding motif, the bacterially expressed 40-kDa subunit binds ATP . The interaction between the 40-kDa subunit and ATP was reduced by th e addition of PCNA. In addition, antibodies raised against the 40-kDa subunit abolished the A1- and PCNA-dependent synthesis of DNA catalyze d by polymerase delta. The putative amino acid sequence of the 40-kDa subunit of A1 revealed significant homology with the bacteriophage T4 gene 44 protein and, to a lesser degree, with the tau and gamma subuni ts of Escherichia coli DNA polymerase III holoenzyme.