3. The dnaB gene of E ool encodes a helcase conae) that nwinds DNA atthe replica

Question

3. The dnaB gene of E ool encodes a helcase conae) that nwinds DNA atthe replicaton fork hs is to incubate the substrates under a variety of condi orsand then on agarose gels. The short single strand move lyrR subject a sample to the longer DNA strand but move much tanieri beenenwoundand detached. The of shorter strand can be folowed selectively by making and examining poston in the gol autoradography. The results of an assay heloase is shown in Figure 2. The substrates are 1 the without tais, was not unwound by Onab and 2 However, when either substrate with tails was incubated at Cwith DnaB and ATP sign ant absolutely dependent on ATP hydrolysa hair-fragment was unwound lane 9) unwinding was (compare lanes 5 and 6 and lanes 9 and 100. minutes after DnaB ctherwise it inhibited unwinding 2. The double stranded DNA egon in substate2 has been substrate 2) circular strand of DNA?

Explanation / Answer

The Dna B helicase is moving along the 5' to 3 ' direction along the previously circular DNA in substrate 3 as evidenced by the presence of the 3' labelled longer fragment in lane 9.

If it was moving in the 3' to 5' direction, then the 5' labelled shorter fragment would have been released.

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