CHARACTERIZATION OF THE SIGNAL RECOGNITION PARTICLE (SRP) RNA POPULATION OF TOMATO (LYCOPERSICON-ESCULENTUM)

Molecular cloning of 30 cDNAs and subsequent characterization of the c orresponding SRP RNA from four cultivars of tomato (Lycopersicon escul entum) revealed altogether 14 sequence variants, which could be ordere d into six groups. The expression of five representatives from these g roups was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) in different cultivars and different tissues. Although one cu ltivar-specific SRP RNA variant could be detected in the leaf SRP RNA population, identical SRP RNA populations seem to be present in the fo ur different cultivars as well as in different tissues, such as leaves , flowers, fruits, stems and roots. Sequence comparison revealed that several variants might have evolved by recombination of two different SRP RNA sequences. On the basis of five SRP RNA variants, the current secondary structure model was refined and a new conserved structural e lement was detected. Comparative sequence analysis of domain II from a ll known SRP RNA homologues reveals a remarkable conservation of this element. As demonstrated previously, the corresponding area overlaps w ith a region that interact with the SRPp68/p72 heterodimer and/or with ribosomes. Based on structural and functional considerations, we prop ose that the domain IV structure together with the highly conserved ar ea of domain II constitutes the essential core of the SRP RNA.