Replicase gene

Sequencing.—With the elucidation of the primary and secondary structure of the replicase gene, the complete 3569-nucleotide-long sequence of the RNA of bacteriophage MS2 is now known.153 This is the first organism for which theentire nucleic acid structure has been elucidated, and Fiers and his group richly deserve their bouquet. 

One subunit (Mr 65,000) is the product of the replicase gene encoded by the viral RNA and has the active site for replication. The other three subunits are host proteins normally involved in host-cell protein synthesis the E. coli elongation factors Tu (Mt 30,000) and Ts (Mr 45,000)... 

A., Volckaert, G., and Ysebaert, M. (1976) Complete nucleotide-sequence of bacteriophage MS2-RNA - primary and secondary structure of replicase gene. Nature, 260, 500-507. 

Human a-globin Human 3 globin Human Y globin2 Human e-globin Rabbit a-globin Rabbit 3 globin Chicken ovalbumin MS2 Replicase gene Embryonic mouse Rat preproinsulin E.coli 16S ribosomal... 

As noted, the viral RNA is of the plus (+) sense. Replicase synthesizes RNA of minus (-) sense using the infecting RNA as template. After minus RNA has been synthesized, plus RNA is made from this minus RNA. The newly made plus RNA strands now serve as messengers for virus protein synthesis. The gene for the maturation protein is at the 5 end of the RNA. Translation of the gene coding for the maturation protein (needed in only one copy per virus particle), occurs only from the newly formed plus-strand RNA as... 

Figure 29-17 Partial sequence and secondary structure model of RNA of bacteriophage MS2. The initiation and termination codons for each of the three genes (A protein, coat protein, and replicase) are enclosed in boxes as is the second stop signal that is in-frame for the A protein gene but out-of-frame for the coat protein gene. The entire coat protein gene is shown but less them one-third of the entire sequence is given. From W. Fiers and associates.499-501...

A more accurate replication required protein enzymes, but the synthesis of these enzymes required a primitive translation apparatus, and therefore the presence of genes for such an apparatus. The smallest genome that is capable of coding for a replicase and a rudimentary translation apparatus is not known, but it has been estimated that a minimum of ten genes is necessary in order to keep translation errors within tolerable limits. The appearance of a primitive genome presents, however, two contrasting problems. 

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