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The SMUG1 gene codes for the enzyme single-strand selective monofunctional uracil DNA glycosylase. This enzyme can remove uracil from single-strand (unpaired) DNA. (Uracil can occur in DNA due to deamination of cytosine.)

What happens when this enzyme removes uracil? It seems what would be best is that a cytosine would replace the uracil in the DNA strand to restore the original DNA sequence, but I haven't found mention of this. The alternatives would seem to be that the enzyme simply splits the strand into two strands by removing the uracil (which are then unconnected since this is single-strand DNA), or it joins the two adjacent bases together, deleting the uracil but keeping the strand intact.

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I think you needed to click just one more link: https://en.wikipedia.org/wiki/Base_excision_repair

It just cuts out the base so there's an empty spot on the ribose. I was looking for a picture and the top hit was actually this site (at A):

What is the mechanism of monofunctional glycosylases?

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  • $\begingroup$ Yes, I now see SMUG1 just removes the base, leaving the sugar and phosphate. It seems then that the information that U had been present (and thus cytosine is appropriate) is lost. The fate of the baseless sugar-phosphate is unclear to me from the Wikipedia articles; most of the discussion seems to suggest that breaking of the phosphate backbone is usual (which would leave two unconnected DNA molecules). $\endgroup$ – mgkrebbs Oct 2 '16 at 18:55

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