CCA1 IS REQUIRED FOR FORMATION OF GROWTH-ARRESTED CONFLUENT MONOLAYEROF RAT 3Y1 CELLS

A novel cDNA fragment, named cca1 (confluent 3Y1 cell-associated 1), w as previously isolated on the basis of preferential accumulation of th e corresponding mRNA in growth-arrested confluent but not in growing s ubconfluent rat 3Y1 cells, The cca1 cDNA was found to consist of 5022 nucleotides with an open reading frame of 1905 nucleotides, encoding a protein of 635 amino acids. Unlike the 3Y1 cell case, cca1 mRNA was n ot detected in confluent 3Y1 BU, 3Y1 BU/pTK, 3Y1-16E6, or F2408 cells, whose growth patterns monitored by phalloidin staining and bromodeoxy uridine incorporation were different from those of the confluent 3Y1. cells. A restoration of the confluent 3Y1-type growth pattern was obse rved in the cca1 cDNA-introduced 3Y1 BU and 3Y1 BU/pTK cells after rea ching confluence but not in the cDNA-introduced 3Y1-16E6 or F2408 cell s, The results allow us to conclude that cca1 is required but not suff icient for formation of growth-arrested confluent monolayer of 3Y1 cel ls.