MTS1, which encodes a protein named p16, is an important gene involved in tumorigenesis. To increase the expression of p16 in Escherichia coli, MTS1 was synthesized de novo by recursive PCR, with codons optimized towards E coli. Studies indicate that N-terminal amino acids of p16 had negative impact on its expression in E coli. The function of p16DeltaN8 is not affected by the absence of N-terminal eight amino acids, compared with p16. p16DeltaN8 was expressed in E coli, which reached 22% of total cell proteins. Purified p16DeltaN8 (purity was 98%) was delivered into A875 (melanoma), MCF7 (breast cancer), and HeLa (cervical cancer) cells by lipofectin. Results show purified p16DeltaN8 remarkably inhibited the growth of A875 and MCF7 cells, whereas it had little effect on HeLa cells. (C) 2004 Elsevier Inc. All rights reserved.