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Abstract
Initiation of transcription of favored templates by Q beta replicase requires a much lower GTP concentration than does transcription of templates that are selected against. Although the enzyme requires a high GTP concentration to initiate transcription of Q beta RNA, the presence of the host factor substantially reduces the GTP concentration requirement. In addition, the Q beta replicase preparation must contain ribosomal protein S1 for initiation to occur at low GTP. Mn2+ ions, which can substitute for host factor in Q beta RNA replication in vitro, and which reduce the template specificity of Q beta replicase, also reduce the GTP requirement for initiation. But while Mn2+ ions produce this effect with all templates, host factor is specific for Q beta RNA. When both host factor and Mn2+ are present, transcription of Q beta RNA occurs at a much lower GTP concentration. Thus, host factor and Mn2+ appear to reduce the GTP concentration requirement by different mechanisms.
Highlights
Initiation of transcription of favored templabtyesQi3 polypeptide, host factor, is a heat-stable, RNA-binding proreplicaserequiresa much lower GTP concentration tein, requiredfor transcription of &p R N A only [6].B0t.h than does transcription of templates that are selected S1 and HF’ have been shown to be required for initiationof against.Althoughtheenzymerequiresa high GTP R N A synthesis and to bind to particular sequences on Qp concentration to initiate transcriptionof Qp RNA, the R N A [5,6,7]
Effect of Host Factor and Mn-We have found previously that Mn”, whichreduces the template specificity of Qp replicase, reducesthe GTP requirement for initiatiofntran
RNA polymers [3].Since Mn2+has previously been shownto allow in vitro Q p RNA replication in the absence of host factor [4], we measured the GTPrequirement for initiation of
Summary
Mn2+ions, which can substitute forhost factor inQ/3 RNA replication in u i t m , and which reduce the template specificity of QB replicase, reduce the GTP requirement for initia-. We show that this effect is specific for Qp. RNA, and that the presence of 30 S ribosomal protein SI is necessary forhost factor to reducethe GTP requirement. While Mn2+ions produce this effect with all EXPERIMENTALPROCEDURES templates, host factor is specific for Q/3 RNA. When both host factor and Mn2+ arepresent, transcription of. Enzyme present with poly(C) astemplate when aurintricarboxylic acid was added after initiation to prevent reinitiation This enzyme was free of host factor activity as measured by stimulation of in vitro
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