FRAMESHIFT MISMATCH RECOGNITION BY THE HUMAN MUTS-ALPHA COMPLEX

DNA mismatch binding by an extensively purified hMutS alpha mismatch r ecognition complex was investigated using a bandshift assay. The compl ex bound to G . T mispairs and to looped structures containing an unpa ired single or two adjacent bases. A CA loop was preferentially recogn ised if the unpaired bases formed part of a repeated sequence. In gene ral, single base loops were also more favourably recognised by hMutS a lpha when present in monotonic runs of two to five. In one series of s ubstrates, based on a known hotspot for frameshift mutations in the hy poxanthine-guanine phosphoribosyltransferase gene, in which different length G, A, C or T tracts were flanked by closely similar sequences, an A loop was bound preferentially in the absence of adjacent As and a C loop in the absence of adjacent Cs. This preferential binding was i nfluenced by the base immediately 5' to the loop. Thus, while repeated regions generally favour recognition of single base loops by hMutS al pha, other factors related to local sequence may influence this intera ction. (C) 1998 Elsevier Science B.V. All rights reserved.