Question

Question 1a:

How many sigma factors have been identified to be active in the sporulation of B. subtilis? What is each function?

Question 1b:

What is the Lytic Cycle and the Lysogenic cycle? Is it possible to enter the lytic cycle once a phage is in the lysogenic cycle?

Question 1c:

Explain the competition between the Cro repressor and the lambda repressor?

Answer 1

1a.Bacillus subtilis indicate that sporulation is primarily controlled at the transcriptional level by four sporulation-specific sigma factors, σ^F, σ^E, σ^G, and σ^K . These sigma factors are essential for sporulation. σ^G couples its transcriptional program to morphological changes.

b. The lytic cycle involves the reproduction of viruses using a host cell to manufacture more viruses; the viruses then burst out of the cell. The lysogenic cycle involves the incorporation of the viral genome into the host cell genome, infecting it from within. In the lysogenic cycle, the phage DNA first integrates into the bacterial chromosome to produce the prophage. The daughter cells can continue to replicate with the prophage present or the prophage can exit the bacterial chromosome to initiate the lytic cycle.

c. Repressor and cro compete for control of an operator region containing three operators that determine the state of the lytic/lysogenic genetic switch. If this competition is won by a repressor, transcription of the cro gene is blocked and repressor transcription is maintained. Lysogeny will result. A competition won by cro, however, means that the late genes of phage l will be expressed; this will result in lysis. In this case, cro blocks transcription that occurs from P_RM, the promoter that is responsible for the maintenance of repressor transcription.