Alternative splicing and mitochondrial import: Kubo, N., Harada, K., Hirai, A. and Kadowaki, K-I. (1999) A single nuclear transcript encoding mitochondrial RPS14 and SDHB of rice is processed by alternative splicing: common use of the same mitochondrial targeting signal for different proteins, Proc. Natl. Acad. Sci. U. S. A. 96, 9207–9211

Abstract

This paper presents evidence that two proteins that function in the mitochondria of rice, but that are otherwise unrelated, have transferred to the nuclear genome and share sequences for targeting to mitochondria. The two genes are rps14, encoding ribosomal protein RPS14, and sdhb, encoding succinate dehydrogenase subunit B. Analysis of their cDNAs revealed that sdhb and rps14 have identical 5′ sequences. The mitochondrial genome still retains a gene with homology to rps14, but it contains internal stop codons, whereas there is no equivalent sdhb sequence. Genomic sequencing revealed that the coding sequence for SDHB is divided into two exons, and, remarkably, the coding sequence for RPS14 is located between these exons. The gene transcripts appear to be carried by a single mRNA with alternative splicing giving rise to the two proteins. These results suggest that gene-transfer of sdhb occurred prior to the migration of rps14, and that rps14 was subsequently able to transfer into an existing nuclear gene and make use of its mitochondrial targeting sequence.