RNA maturation of the rice SPK gene may involve trans-splicing

A gene encoding a calcium-dependent seed-specific protein kinase (SPK) is a bundantly expressed in developing rice seeds (Kawasaki, T, et al. Gene (199 3) 129, 183-189). Rice genomic clones encoding SPK were isolated using the entire cDNA fragment as a probe. Physical mapping of these genomic clones i ndicated that the genomic region corresponding to the entire cDNA was divid ed into two different regions, SPK-A and SPK-B, located on different rice c hromosomes. The results of RACE-PCR analyses showed that the respective tra nscripts from SPK-A and SPK-B contained additional sequences which were not found in the SPK cDNA, and that these sequences were removed like introns during maturation of the SPK mRNA. These results suggest that two different RNAs were independently transcribed from SPK-A and SPK-B and joined, possi bly by trans-splicing.