Replicative form

Budding and release of progeny virus. B. Replicative cycle of an influenza virus, an example of an RNA virus. 1. Attachment. 2. Endocytosis. 3. Influx of H+ through M2 protein. 4. Fusion of the viral envelope with the endosomes membrane, dissociation of the RNP complex, and entry of viral RNA into the nucleus. 5. Synthesis of viral mRNA by viral RNA polymerase. 6. Translation of viral mRNA by host cell s ribosomes. 7. Replication of viral RNA, using viral RNA polymerase, via cRNA replicative form. 8. Assembly of virus particles, and 9. Budding and release of progeny virus. 

The genomes of DNA viruses vary greatly in size (Table 24-1). Many viral DNAs are circular for at least part of their life cycle. During viral replication within a host cell, specific types of viral DNA called replicative forms may appear for example, many linear DNAs become circular and all single-stranded DNAs become... 

Note Data on size of DNA are for the replicative form (double-stranded). The contour length is calculated assuming that each base pair occupies a length of 3.4 A (see Fig. 8-15). 

Canine parvovirus, first identified in 1978, is now endemic.455,456 Childhood fifth disease is also caused by a parvovirus.456,457 When these single-stranded DNA viruses infect cells a double-stranded replicative form of DNA arises by synthesis of the complementary negative strand alongside the original positive DNA strand. Many copies of the replicative form are then synthesized. The negative strands of the replicative forms serve as templates for synthesis of numerous new positive strands that are incorporated into the progeny viruses. The whole process may take only 20 minutes. Some parvoviruses are unable to reproduce unless the cell is also infected by a larger adenovirus. 

Figure 27-20 (A) Hypothetical replisome for concurrent replication of leading and lagging strands by a dimeric polymerase associated with helicase dnaB and a primosome. Open arrows indicate directions of movement of DNA, which is forming a loop as the polymerase fills a gap to complete an Okazaki fragment. The primase will then form a new primer and a new loop. From Komberg and Baker.265 (B) Electron micrograph of the primosome bound to covalently closed ( )X174 duplex replicative form. These enzymatically synthesized duplexes invariably contain a single primosome with one or two associated small DNA loops. From A. Komberg in Hubscher and Spadari,266 pp. 9,10.

For long-term storage at—70°C, bacteria, containing plasmids or phage replicative form are resuspended in 2X TY medium, containing 15% glycerol in... 

Fig. 4.3. Diagram showing the origin of the two single-stranded M13 phage recombinants obtained after cloning a DNA fragment into the double-stranded replicative form of M13.

Restriction enzyme used to cut Ml3mp7 (replicative form) Sequence cleaved Potentially clonoble fragments ... 

Priming with the 96 nucleotide universal primer isolated from an EcoRI digest of Mt3mp2962 replicative form DNA... 

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