Tanakarn MonshupaneeSirirat Fa-AroonsawatWipa ChungjatupornchaiMahidol University2018-08-202018-08-202006-05-01Microbiology. Vol.152, No.5 (2006), 1417-1425135008722-s2.0-33646785377https://repository.li.mahidol.ac.th/handle/20.500.14594/23332The presence of a multicopy chromosome, with each copy containing two rRNA operons (rrnA and rrnB), has been an obstacle to analysing mutated rRNA in Synechococcus PCC 7942. To create a system for expressing homogeneous mutated rRNA, the chromosomal rrn operons were sequentially inactivated and a final strain was successfully obtained with all the chromosomal rrn operons inactivated but carrying a replaceable multicopy plasmid containing a single rrn operon. The lag time required for growth response on dark/light shift of mutant strains with chromosomal rrnA or rrnB inactivated was increased 50 % over that of the wild-type strain; however, the presence of the plasmid-borne rrn operon restored the lag time. The doubling time of mutant strains carrying only a functional rrnB operon, but not strains carrying only a functional rrnA operon, was significantly longer than that of the wild-type strain. A strain in which essentially all the cellular 23S rRNA contained the mutation C2588A was temperature sensitive at 16 °C and 45°C. Position C2588 is equivalent to C2611 of the peptidyltransferase centre in domain V of Escherichia coli 23S rRNA. © 2006 SGM.Mahidol UniversityImmunology and MicrobiologyArticleSCOPUS10.1099/mic.0.28691-0