Microbiology Procedure

Index >> Bacteriophages - Part One >> DNA of Ff Phages

DNA of Ff Phages

	DNA of Ff Phages - The nucleic acid is a covalently closed ssDNA ring even though the virion is a linear filament. The measurements of the MW of Ff -DNA range form 1.7 - 2.5 x 106. The average is 1.90 : 0.07 x 106 for the sodium salt of Ff DNA. This corresponds to 8,740+-210 nucleotides.
The MW of the replicative form (RP) is estimated to be 3.8+- 0.14 x 106. More than one third of the bases of viral DNA are thymine. Ff viral DNAs have pyrimidine tracts of 9-20 base residues. Poly(dA) tracts have also been found in Pi DNA. The pf appears to have one strong and one weak RNA polymerase binding site. The binding sites are protected from nuclease digestion by RNA polymerase.
There are about 40 base pairs in the protected DNA of the first binding site. The binding site is rich in A- T base pairs, and contains a sequence having twofold rotational symmetry. The point of initiation of the RNA transcript is located in the middle of the binding site. The genome consists of eight complementation groups, presumed to correspond to eight genes (1- VIII). The product of gene VIII is the major coat protein, The gene III product is a minor coat protein (A protein), of which there are only 1-2 copies per virus particle.
Genes II and V are concerned with the synthesis of viral DNA. Genes II and IV are separated by an intergenic region. The DNA of this region does not transcribe mRNA. Initiation of complementary strand synthesis begins in this region.

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