ABSTRACT
Several cDNAs encoding ribulose-1,5-bisphosphate carboxylase/oxygenase activase (Rubisco activase, RCA) were isolated from a maize (Zea mays L.) leaf cDNA library. Although all the cDNAs encoded the same polypeptide, the RCA beta isoform, they showed two different downstream-like elements (DST-like) at their 3' untranslated regions (UTRs). The Zmrca1 cDNAs had the subdomain I, and II and the Zmrca2 cDNAs, besides these subdomains, showed two repeats of the subdomain III. The presence of at least two different rca genes in the maize genome was demonstrated by Southern, and by PCR analysis using primers specific for the two cDNAs. Northern analysis with probes specific for each gene showed that the Zmrca2 was expressed as a 1.8 kb transcript, the Zmrca1 corresponded to a 1.4 kb transcript, and a 1 kb band was a stable degradation product of one or both transcripts. Although both mRNAs showed cyclic variations during a day/night period, with their highest levels before dawn, the Zmrca2 transcript showed stronger changes than the Zmrca1 transcript, presenting a twofold larger highest to lowest RNA accumulation ratio than the Zmrca1 transcript, implying that they have different turnover rates. Our results suggest that post-transcriptional mechanisms, mediated by the DST-like element might be involved in the circadian expression of the maize rca transcripts.
