Journal
IMMUNOLOGY AND CELL BIOLOGY
Volume 82, Issue 2, Pages 219-225Publisher
WILEY
DOI: 10.1046/j.0818-9641.2004.01221.x
Keywords
affinity maturation; human DNA polymerase-eta; immunoglobulin variable region genes; reverse transcription; somatic hypermutation
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We have proposed previously that error-prone reverse transcription using pre-mRNA of rearranged immunoglobulin variable (IgV) regions as templates is involved in the antibody diversifying mechanism of somatic hypermutation (SHM). As patients deficient in DNA polymerase-eta exhibit an abnormal spectrum of SHM, we postulated that this recently discovered Y-family polymerase is a reverse transcriptase (RT). This possibility was tested using a product-enhanced RT (PERT) assay that uses a real time PCR step with a fluorescent probe to detect cDNA products of at least 27-37 nucleotides. Human pol-eta and two other Y-family enzymes that are dispensable for SHM, human pols-iota and -kappa, copied a heteropolymeric DNA-primed RNA template in vitro under conditions with substantial excesses of template. Repeated experiments gave highly reproducible results. The RT activity detected using one aliquot of human pol-eta was confirmed using a second sample from an independent source. Human DNA pols-beta and -mu, and T4 DNA polymerase repeatedly demonstrated no RT activity. Pol-eta was the most efficient RT of the Y-family enzymes assayed but was much less efficient than an HIV-RT standard in vitro. It is thus feasible that pol-eta acts as both a RNA- and a DNA-dependent DNA polymerase in SHM in vivo, and that Y-family RT activity participates in other mechanisms of physiological importance.
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