High expression of a 3'----5' exonuclease activity is specific to B lymphocytes.
V(D)J joining, the immunoglobulin heavy-chain (IgH) class switch, and somatic hypermutation directed at variable regions are unique genetic recombination or mutation events which occur during B-cell differentiation. The enzymatic process directing and controlling these events remains obscure. An assay for exonucleolytic activity has been devised, and an exonuclease activity expressed at high levels in normal B lymphocytes has been detected. The high expression of this enzyme is specific to B lymphocytes and may be developmentally regulated. We have partially purified a B-cell-associated nuclease by column chromatography. Using this preparation, we have begun a rigorous analysis of its activity. This activity is a nonprocessive, 3'----5' exonuclease with a requirement for divalent cations. Our studies demonstrate that EDTA, poly(dI-dC), and glycerol are all inhibitory to B-cell-associated exonucleolytic activity. The exonuclease displays sequence preference but no sequence specificity when tested on a variety of native DNA substrates. This nuclease is distinct from other exonuclease activities previously described.
Kenter
A L
AL
Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago 60680.
Tredup
J
J
D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology*; D001483:Base Sequence; D002478:Cells, Cultured; D004247:DNA; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000235:genetics; D013379:Substrate Specificity
D004247:DNA; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V