The molecular size of Pseudomonas aeruginosa bacteriophage PP7 RNA has been estimated by electron microscopy and polyacrylamide gel electrophoresis. The length of the genome is estimated to be 1.16 μm, similar to R17 RNA (1.22 μm). After formaldehyde treatment under conditions in which R17 RNA has an estimated molecular weight of 1.3 × 106, the molecular weight of the PP7 genome is 1.24 × 106. Without formaldehyde treatment, under conditions in which R17 RNA has an apparent molecular weight of 1.1 × 106, PP7 RNA molecular weight is calculated as 1.03 × 106. PP7 RNA is therefore a very similar size to Group I Escherichia coli RNA bacteriophage genomes, being only 6% smaller than R17 RNA, but about 20% smaller than Group III Qβ RNA. This molecular size is consistent with the suggestion that the PP7 genome has only three cistrons. © 1975.
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