Two distinct cDNAs encoding carbonic anhydrase (CA) were isolated from a maize
λgt 11 library. One of these cDNAs, CA1, which consists of a
5´-leader sequence, three repeat sequences and a 3´-non-coding
region, 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 containing a
276 bp insert compared to CA1, two repeat sequences and a 3´-non-coding
region, is predicted to encode an open reading frame for a polypeptide of 59.2
kDa. Nucleotide sequence alignment analysis indicates that the two repeat
sequences of CA2 are homologous with repeat sequences 1 and 3 of CA1,
respectively.
Four protein bands, with apparent molecular masses of 52, 47, 28 and 27 kDa,
were evident in western blot analyses of crude extracts of maize leaf tissue
prepared in the absence of Triton X-100 and two protein bands, with apparent
molecular masses of 27 and 28 kDa, were detected in western blots of crude
extracts prepared in the presence of Triton X-100. These results indicate
either that both CA1 and CA2 mRNAs are only partially translated, that the CA1
and CA2 proteins are processed, or a combination of both of these
alternatives. Two maize leaf CA1 and CA2 mRNAs detected on northern blots are
longer than any other plant CA mRNA reported to date. Possible roles for the
two CA isozymes in maize leaves are discussed.
The Distribution of Carbonic Anhydrase and Ribulose Diphosphate Carboxylase in Maize Leaves