A temperature sensitive mutant was derived from
Bacillus subtilis Marburg strain. The characters of this mutant were as follows:
(1) The temperature sensitive mutational site was located near the
SM locus on the chromosome.
(2) When incubated at 50°C, the cells ceased growth in one hour, and lost viability thereafter.
(3) When the cells were preincubated at 50°C for 30min and thereafter incubated at 37°C, active alkaline phosphatase [EC 3. 1. 3. 1] was not formed.
(4) When 70-S ribosomes from the mutant cells were treated at 50°C for 10-20min, they were dissociated into 50 S and 30 S to a greater extent than those of parental strain, as judged from sedimentation profiles in the sucrose density gradient centrifugation.
(5) When the ribosomes were treated with ribonuclease [EC 2. 7. 7. 16] after heat treatment at 50°C for 5-10min in the presence of 2×10
-4M Mg
2+, more acid-soluble materials were produced than those of parental strain.
(6) When the ribosomes were treated at 45°C or 50°C for 2-5min, activity of polypeptide synthesis (incorporation of
14C-phenylalanine directed by poly U) was lost to a greater extent than those of parental strain. For example, by heating at 50°C for 2min, 75% of the activity was lost in the mutant while less than 50% was lost in the parental strain.
It was concluded from these results that the mutant isolated might produce temperature sensitive ribosomes.
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