CHARACTERIZATION OF 2 CDNA ENCODING CARBONIC-ANHYDRASE IN MAIZE LEAVES

Two distinct cDNAs encoding carbonic anhydrase (CA) were isolated from a maize lambda gt 11 library. One of these cDNAs, CA1, which consists of a 5'-leader sequence, three repeat sequences and a 3'-non-coding r egion, is predicted to encode an open reading frame for a polypeptide of 71.3 kDa. The other cDNA, CA2, which has a 5'-leader sequence conta ining a 276 bp insert compared to CA1, two repeat sequences and a 3'-n on-coding region, is predicted to encode an open reading frame for a p olypeptide of 59.2 kDa. Nucleotide sequence alignment analysis indicat es that the two repeat sequences of CA2 are homologous with repeat seq uences 1 and 3 of CA1, respectively. Four protein bands, with apparent molecular masses of 52, 47, 28 and 27 kDa, were evident in western bl ot analyses of crude extracts of maize leaf tissue prepared in the abs ence of Triton X-100 and two protein bands, with apparent molecular ma sses of 27 and 28 kDa, were detected in western blots of crude extract s prepared in the presence of Triton X-100. These results indicate eit her that both CA1 and CA2 mRNAs are only partially translated, that th e CA1 and CA2 proteins are processed, or a combination of both of thes e alternatives. Two maize leaf CA1 and CA2 mRNAs detected on northern blots are longer than any other plant CA mRNA reported to date. Possib le roles for the two CA isozymes in maize leaves are discussed.