EFFECT OF TEMPERATURE ON IN-VIVO PROTEIN SYNTHETIC CAPACITY IN ESCHERICHIA-COLI

In this report, we examine the effect of temperature on protein synthe sis, The rate of protein accumulation is determined by three factors: the number of working ribosomes, the rate at which ribosomes are worki ng, and the rate of protein degradation. Measurements of RNA/protein r atios and the levels of individual ribosomal proteins and rRNA show th at the cellular amount of ribosomal machinery in Escherichia coli is c onstant between 25 and 37 degrees C. Within this range, in a given med ium, temperature affects ribosomal function the same as it affects ove rall growth. Two independent methodologies show that the peptide chain elongation rate increases as a function of temperature identically to growth rate up to 37 degrees C. Unlike the growth rate, however, the elongation rate continues to increase up to 44 degrees C at the same r ate as between 25 and 37 degrees C, Our results show that the peptide elongation rate is not rate limiting for growth at high temperature. T aking into consideration the number of ribosomes per unit of cell mass , there is an apparent excess of protein synthetic capacity in these c ells, indicating a dramatic increase in protein degradation at high te mperature, Temperature shift experiments show that peptide chain elong ation rate increases immediately, which supports a mechanism of heat s hock response induction in which an increase in unfolded, newly transl ated protein induces this response, In addition, we find that at low t emperature (15 degrees C), cells contain a pool of nontranslating ribo somes which do not contribute to cell growth, supporting the idea that there is a defect in initiation at low temperature.