Differential Screening by SSH: Suppression Subtractive Hybridization
Suppression Subtractive Hybridization (SSH) is a differential screening method used along with PCR. The objective is to suppress the mRNAs common to two samples or two cell types in order to create simplified subpopuld.lions containing only the mRNAs expressed differentially between the initial samples. Very similar to RDA (see Profile 20), SSH is distinguished essentially by a standardization step between the abundant sequences and those that are very rare, which is designed to favour the detection of mRNAs that are less abundant. It is based simultaneously on the kinetics of reassociation of DNA strands (abundant fragments will hybridize more quickly than rare fragments) and on the existence of the suppressor effect of PCR. This effect is due to the fact that long reverse (complementary) adaptors placed on either side of a single strand will have greater affinity for each other than for a shorter amplification primer. When these long reverse adaptors recognize each other, they form non-amplifiable hairpin structures.