Abstract
Polynucleotide phosphorylase (PNPase) has been studied in detail since its discovery in 1955 [1]. In an attempt to determine what role, if any, it has in mRNA decay in Escherichia coli, we have isolated and characterized a temperature-sensitive mutation, pnp-200, in the pnp gene. In vitro phosphorolysis, polymerization and exchange activities of the partially purified Pnp-200 enzyme are all reduced to 30–40% of wild-type activity at 50°C compared to 32°C. The pnp-200 mutation alone does not affect cell growth or mRNA stability. A triple mutant strain containing pnp-200 in combination with other temperature-sensitive mutations in genes known to affect mRNA metabolism ( rnb-500 and ams-l) is conditionally lethal and shows increased mRNA stability after shift to the non-permissive temperature.
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