Kinetics of cca1, cca2, cca3 and rat gas1 mRNA levels were compared with those of DNA synthesis level in regenerating rat liver cells after partial hepatectomy. A transient decrease of cca3 mRNA level and an increase of rat gas1 mRNA level were observed before initiation of DNA synthesis, followed by a rapid decrease of rat gas1 mRNA level. By molecular cloning and nucleotide sequencing, cca3 cDNA was found to consist of 4514 nucleotides with a large open reading frame of 3027 nucleotides, encoding a protein of 1009 amino acids with three copies of an ankyrin repeat-like sequence.