Question

28. Before replication of the M13 genome, what step is required?

29. How does phage M13 exit the host cell?

Answer 1

28. Before replication of the M13 genome when the Viral (+) strand DNA enters cytoplasmo complementary(-) strand is synthesized by bacterial enzymes then DNA Gyrase, a type II topoisomerase, acts on double-stranded DNA and catalyzes formation of negative supercoils in double-stranded DNA. Final product is parental replicative form (RF) DNA. A phage protein, pII, nicks the (+) strand in the RF and replication initiates.

29.Filamentous phages like M13 bacteriophage are released by a concerted mechanism of assembly and secretion called extrusion. The neosynthesized virions are exported as they got assembled at the cell surface in a secretory process which leaves the host cell fully viable. Extrusion requires three non-capsid proteins, two of them allowing translocation through the inner membrane (IM) and one secretin-like protein forming the transmembrane channel in the outer membrane (OM).

A viral single-stranded DNA binding protein coats around the progeny viral DNA molecules to generate the intracellular precursor for assembly of phage particles. The five structural proteins of the virus are anchored in the inner membrane before their incorporation into the phage particle. As assembly proceeds, the phage genome traverses the inner and outer membranes until the entire DNA molecule has been coated and extruded.