Use of PCR to screen for promoter elements in genomic DNA library clones

We report a modified PCR strategy to screen for promoter elements of genes of interest that is based upon consecutive rounds of PCR and appropriate subcloning. Following preliminary identification and sequencing of intron 1 by standardized PCR, the application of a suited cDNA/intron primer combination renders a succeeding PCR-mediated screening of cosmid or P1-derived artificial chromosome (PAC) libraries possible, thus identifying genomic clones comprising the searched promoter elements. We tested our approach in comparison with a commercially available promoter finder kit by searching the promoter elements of the CENP-C gene from the human and mouse genomes. Applying the kit system, we amplified the anticipated promoter from mouse, but failed in isolating human promoter elements. Our approach made use of a 5'-UTR/intron 1 primer combination in the second round of PCR, enabling the identification of positive clones from genomic DNA within a human PAC library possible. Subcloning and final PCR amplification revealed the successful isolation of the human promoter. Therefore, we conclude that our approach might represent a helpful alternative to identify promoter elements, especially when prior art genome walking, STS-based strategies or anchored PCR failed

Cellular expression of human centromere protein C demonstrates a cyclic behavior with highest abundance in the G1 phase.

Centromere proteins are localized within the centromere-kinetochore complex, which can be proven by means of immunofluorescence microscopy and immunoelectron microscopy. In consequence, their putative functions seem to be related exclusively to mitosis, namely to the interaction of the chromosomal kinetochores with spindle microtubules. However, electron microscopy using immune sera enriched with specific antibodies against human centromere protein C (CENP-C) showed that it occurs not only in mitosis but during the whole cell cycle. Therefore, we investigated the cell cycle-specific expression of CENP-C systematically on protein and mRNA levels applying HeLa cells synchronized in all cell cycle phases. Immunoblotting confirmed protein expression during the whole cell cycle and revealed an increase of CENP-C from the S phase through the G2 phase and mitosis to highest abundance in the G1 phase. Since this was rather surprising, we verified it by quantifying phase-specific mRNA levels of CENP-C, paralleled by the amplification of suitable internal standards, using the polymerase chain reaction. The results were in excellent agreement with abundant protein amounts and confirmed the cyclic behavior of CENP-C during the cell cycle. In consequence, we postulate that in addition to its role in mitosis, CENP-C has a further role in the G1 phase that may be related to cell cycle control