We report here the construction of a homozy-gous rec A460::cam insertion mutant of Synechocystis sp.PCC 6803 that may be useful for plant Molecular genetics by providing a plant like host free of interfer-ence from homologous recombination. The homozygous rec A460::cam mutant is highly sensitive to UVC under both photoreactivating and nonphotoreactivating con-ditions compared to the wild type (WT). The liquid culture of the mutant growing in ~800 lx accumulates nonviable cells to the tune of 86% as estimated by col-ony counts on plates incubated at the same temperature and light intensity. The generation time of recAmutant in standard light intensity (2,500 lx) increases to 50 h compared to 28 h in lower light intensity (~800 lx) that was used for selection, thus explaining the earlier failures to obtain a homozygous recA mutant. The WT, in contrast, grows at faster rate (23 h generation time) in standard light intensity compared to that at ~800 lx(26 h). The Synechocystis RecA protein supports homologous recombination during conjugation in recA^— mutant of Escherichia coli , but not the SOS response as measured by UV sensitivity. It is suggested that using this homozygous rec A460::cam mutant,investigations can now be extended to dissect the network of DNA repair pathways involved in housekeeping activities that may be more active in cyanobacteria than in heterotrophs. Using this mutant for the first time we provide a genetic evidence of a mechanism independent