| dc.description.abstract | The integrity of the genetic material of all organisms is assaulted continuously by a
multitude of endogenous and exogenous agents throughout its lifetime, where the DNA bases
of the genetic code may be altered if not repaired properly before replication causing cellular
malfunction, cell death or cancer. Uracil (U), which is a normal base in RNA, arises in DNA
by hydrolytic deamination of cytosine (C) or by erroneous incorporation of deoxyuridine
monophosphate opposite adenine (A) during replication. Other damaging events is caused by
reactive oxygen species (ROS) generated during aerobic metabolism, as e.g., oxidation of
thymine (T) into 5-hydroxymethyluracil (hmU), which may disrupt normal gene expression if
left unrepaired. Cells have developed a multitude of repair mechanisms to correct each type of
DNA damage, where uracil-DNA glycosylases (UDGs) repair U and U-derivatives by
initiating the base excision repair (BER) pathway. One UDG is single-strand selective
monofunctional uracil-DNA glycosylase (SMUG1), which excises U and hmU from DNA in
addition to several other bases because of its flexible active site. In the study we found that
replacing certain residues (Ser26/Glu35 and Pro240) in human SMUG1 eliminated the
excision activity for hmU in single-stranded (ss) DNA, while the excision activity for uracil
was retained in ssDNA, bubble DNA and R-loop DNA as demonstrated using commercial as
well as our own purified enzyme. This is the first study showing the importance of these
amino acid residues for the excision of hmU from DNA by SMUG1. | |