Effect of primer proximity to a difficult-to-sequence region on read length and sequence quality.

Anecdotal and not well-established evidence implies that there could be some effect of primer proximity in relation to a difficult region on read length and sequence quality. In this paper we sequenced many different categories of difficult regions where primers were located at various distances in relation to such regions and we found that there is only weak, if any, correlation between primer proximity and read length or sequence quality. The occasional improvements observed in some studies could be related instead to more optimal primers or better quality DNA. We suggest that instead of trying to design primers at varying distances to a difficult region, sequence finishers concentrate on applying modified chemistries appropriate to a given difficult region.