A method for simultaneous RNA and DNA isolation from dried blood and semen stains.

The origin of forensic stains can be determined by detection of cell- and tissue-specific messenger-RNA (mRNA) using reverse transcription-polymerase chain reaction (RT-PCR) as demonstrated recently by the authors. However, in cases with limited sample amount DNA analysis has priority in routine forensic laboratory work. The objective of this study was to develop an easy-to-perform method for the simultaneous isolation of RNA and DNA from the same sample. Due to the common nucleic acid structure RNA and DNA isolation procedures are very similar. The investigation of blood and semen stains has shown that DNA suitable for STR analysis can be recovered by ethanol precipitation after acid phenol/chloroform extraction and removal of RNA. Although the sensitivity of this method is lower than direct DNA isolation with chelex extraction, it is sufficient for most cases as experiments with highly diluted stains have demonstrated. This time- and cost-saving method therefore may be useful when RNA and DNA analysis have to be performed from the same sample.