Question

The genetic material of $M_{13}$ bacteriophage is
A. ds DNA
B. ds RNA
C. ss RNA
D. ss DNA

Answer 1

Hint:
$M_{13}$ is a chronic phage, releasing its progeny without killing the host cells. The infection causes turbid plaques in E. coli lawns, of intermediary opacity in comparison to regular lysis plaques. $M_{13}$ plasmids are used for many recombinant DNA processes, and the virus has also been used for phage display, directed evolution, nanostructures, and nanotechnology applications.

Complete answer:
$M_{13}$ is a filamentous bacteriophage composed of circular single-stranded DNA (ssDNA) which is 6407 nucleotides long encapsulated in approximately 2700 copies of the major coat protein, and capped with 5 copies of two different minor coat proteins on the ends. The minor coat protein attaches to the receptor at the tip of the F pilus of the host Escherichia coli. The phage coat is primarily assembled from a 50 amino acid protein, which is encoded by gene VIII in the phage genome. There are four other proteins on the phage surface. At one end of the filament are five copies of the surface exposed pIX and a more buried companion protein, pVII. If p8 forms the shaft of the phage, p9, and p7 form the "blunt" ends. These proteins are very small, containing only 33 and 32 amino acids respectively, though some additional residues can be added to the N-terminal portion of each which are then presented on the outside of the coat. At the other end of the phage particle are five copies of the surface exposed pIII and its less exposed accessory protein, pVI. These form the rounded tip of the phage and are the first proteins to interact with the E. coli host during infection.

Hence, the correct option is (D) ss DNA.

Note: Phage proteins in the cytoplasm are pII, pX, and pV, and they are part of the replication process of DNA. The other phage proteins are synthesized and inserted into the cytoplasmic or outer membranes.