The activation-induced cytidine deaminase (AID) efficiently targets DNA in nucleosomes but only during transcription.
The activation-induced cytidine deaminase (AID) initiates somatic hypermutation, class-switch recombination, and gene conversion of immunoglobulin genes. In vitro, AID has been shown to target single-stranded DNA, relaxed double-stranded DNA, when transcribed, or supercoiled DNA. To simulate the in vivo situation more closely, we have introduced two copies of a nucleosome positioning sequence, MP2, into a supercoiled AID target plasmid to determine where around the positioned nucleosomes (in the vicinity of an ampicillin resistance gene) cytidine deaminations occur in the absence or presence of transcription. We found that without transcription nucleosomes prevented cytidine deamination by AID. However, with transcription AID readily accessed DNA in nucleosomes on both DNA strands. The experiments also showed that AID targeting any DNA molecule was the limiting step, and they support the conclusion that once targeted to DNA, AID acts processively in naked DNA and DNA organized within transcribed nucleosomes.
Shen
Hong Ming
HM
Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
Poirier
Michael G
MG
Allen
Michael J
MJ
North
Justin
J
Lal
Ratnesh
R
Widom
Jonathan
J
Storb
Ursula
U
D000668:Ampicillin Resistance / Q000235:genetics; D003564:Cytidine Deaminase / Q000378:metabolism*; D004247:DNA / Q000235:genetics*; D004277:DNA, Single-Stranded / Q000235:genetics; D004278:DNA, Superhelical / Q000235:genetics; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007134:Immunoglobulin Switch Region / Q000235:genetics; D007136:Immunoglobulins / Q000235:genetics; D009707:Nucleosomes / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D015183:Restriction Mapping; D027041:Somatic Hypermutation, Immunoglobulin; D014158:Transcription, Genetic; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D006657:Histones; D007136:Immunoglobulins; D009707:Nucleosomes; D004247:DNA; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase