Defective assembly of the small ribosomal subunit in a temperature-sensitive mutant of Escherichia coli. Experiments in vitro

Comparison of the properties in vitro of total 30-S ribosomal subunit proteins and purified protein S4 of Escherichia coli D10 (wild type) and E. coli 219ts2(temperature-sensitive) has given the following results. 1. Reconstitution of functional 30-S subunits in vitro occurs when total 30-S subunit proteins of either strain are used even at temperatures which are not permissive for 30-S subunit assembly in vivo in E. coli 219ts2. The yield of reconstitution is, however, twofold lower with 30-S subunit proteins of E. coli 219ts2 than with wild-type proteins. 2. The yield of complex formation between 16-S rRNA and protein S4 of E. coli 219ts2 is temperature-sensitive and lower at all temperatures tested (33-42 degrees C) than that observed when wild-type S4 is used. 3. The conformational stability of complexes between 16-S rRNA and S4 from 219ts2 is more temperature-sensitive than that of analogous complexes containing wild-type S4. These observations provide an explanation for the temperature sensitivity of 30-S subunit assembly in E. coli 219ts2.