Question

1. During the past several decade's significant progress has been made in our understanding of the process of DNA replication in eukaryotes.  Although the basic mechanisms of replication are similar to prokaryotes, significant differences are also apparent.  In contrast to prokaryotes where a single DNA directed DNA polymerase (pol III) catalyzes the formation of both leading and lagging strands, two distinct DNA directed DNA polymerases catalyze leading and lagging strand syntheses in eukaryotes. The features of these two replicates are listed below.

	Pol alpha	Pol Beta
Catalytic polypeptide	165 kD	125 kD
Associated Enzyme Activities
Tightly bound primase	Yes	No
3’-->5’ exonuclease	No/yes*	Yes
5’-->3' exonuclease	No	No
Processivity	Moderate	Very high

                              *depends on the source of the enzyme

a.  Describe/diagram what is meant by leading and lagging strands.  

b. Based on the information given above, which polymerase catalyzes the leading strand synthesis?  Which catalyzes lagging strand synthesis?   Which property or properties of the enzymes are relevant to your answer?  Why?  Explain in detail.

2. Sigma protein by itself cannot bind to promoters.  Predict the effect of a mutation enabling sigma to bind to the –10 region in the absence of other subunits of RNA polymerase.

Answer 1

Solution:

2) The binding of mutant sigma to the -10 lement withot other subunits in the holoenzyme would inhibit the binding of core polymerase to the Dna and activate the preinitiation complex formation and initiation of transcription. So initiation from this promoter will not takes place.