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Abstract Background Deproteinized DNA from eukaryotic and prokaryotic cells still contains a low-molecular weight peptidic fraction which can be dissociated by alkalinization of the medium. This fraction inhibits RNA transcription and tumor cell growth. Removal from DNA of normal cells causes amplification of DNA template activity. This effect is lower or absent in several cancer cell lines. Likewise, the amount of active peptides in cancer cell DNA extracts is lower than in DNA preparation of the corresponding normal cells. Such evidence, and their ubiquitous presence, suggests that they are a regulatory, conserved factor involved in the control of normal cell growth and gene expression. Results We report that peptides extracted from wheat bud chromatin induce growth inhibition, G2 arrest and caspase-dependent apoptosis in HeLa cells. The growth rate is decreased in cells treated during the S phase only and it is accompanied by DNA damage and DNA synthesis inhibition. In G2 cells, this treatment induces inactivation of the CDK1-cyclin B1 complex and an increase of active chk1 kinase expression. Conclusion The data indicate that the chromatin peptidic pool inhibits HeLa cell growth by causing defective DNA replication which, in turn, arrests cell cycle progression to mitosis via G2 checkpoint pathway activation.

Three peptides were isolated from bovine seminal plasma and purified to homogeneity. The amino acid sequences, as determined by FAB mass spectrometry, are the following: pGlu-Ala-Glu-Ser-Asn-OH, pGlu-Ala-Glu-Ser(PO3H2-Asn-OH and pGlu-Val-Gly-Glu-Ser-Glu-Asn-OH. These three peptides and some of their analogues were synthesized using liquid- and solid-phase techniques. The pentapeptide pGlu-Ala-Glu- Ser-Asn-OH showed a remarkable affinity for kinase NII and a strong inhibiting activity in DNA transcription. These findings support the hypothesis that phosphorylated acidic domains of nuclear non-histone proteins could bind to DNA, thereby controlling transcription.