transcriptional activity at supraoptimal temperature of growth in the antarctic psychrotrophic bacterium pseudomonas syringae transcriptional activity was monitored in cells of the antarctic psychrotrophic bacterium pseudomonas syringae lz4w which does not grow above 30 degrees c it was observed that the bacterium was capable of synthesising rna at a temperature range of 037 degrees c both in vitro and in vivo the net incorporation of the radioactive precursor 3huridine into rna was found to be affected at 37 degrees c a pulsechase experiment following a 32p labeling of rna in vivo indicated that the ribosomal rnas rrnas degrade faster at and above 30 degrees c it was also found that the increased ribonuclease rnase activity at high temperature might be responsible for this degradation the attack on ribosomal rnas by rnase took place after their assembly into ribosomal particles it is suggested that the degradation of rrnas at supraoptimal temperatures might be a detrimental factor for growth above 30 degrees c