Reportedly, in human immunodeficiency virus type I (HIV) vectors, insertion of central polypurine tract (cPPT) increased expression of transgenes for a short period. To test this for a stable condition, we constructed a series of vectors carrying a Neo' gene as a stable marker driven by a synthetic thymidine kinase (hTK) promoter. Transduction efficiency was increased in about 2-fold and decreased in about 8-fold by insertion of the reported 178 bp and our 282 bp cPPTs, respectively. PCR analyses revealed that insertion of 282 bp cPPT, but not 178 bp cPPT, impaired integration, although it did not deteriorate nuclear transport much. Furthermore, we found that insertion of 282 bp cPPT between hTK promoter and an upstream LTR sequence reduced reporter gene activity in about 5-fold. This inhibitory effect of 282 bp cPPT may partly account for the observed decrease in transduction efficiency. We suggest that actual effect of cPPT insertion should be examined in each HIV vector. (C) 2003 Elsevier Science (USA). All rights reserved.