A novel cDNA fragment, named cca1 (confluent 3Y1 cell-associated 1), was previously isolated on the basis of preferential accumulation of the corresponding mRNA in growth-arrested confluent but not in growing subconfluent 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 not detected in confluent 3Y1 BU, 3Y1 BU/pTK, 3Y1-16E6, or F2408 cells, whose growth patterns monitored by phalloidin staining and bromodeoxyuridine incorporation were different from those of the confluent 3Y1 cells. A restoration of the confluent 3Y1-type growth pattern was observed in the cca1 cDNA-introduced 3Y1 BU and 3Y1 BU/pTK cells after reaching confluence but not in the cDNA-introduced 3Y1-16E6 or F2408 cells. The results allow us to conclude that cca1 is required but not sufficient for formation of growth- arrested confluent monolayer of 3Y1 cells.
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