High frequency of +1 programmed ribosomal frameshifting in Euplotes octocarinatus

Programmed −1 ribosomal frameshifting (−1 PRF) has been identified as a mechanism to regulate the expression of many viral genes and some cellular genes. The slippery site of −1 PRF has been well characterized, whereas the +1 PRF signal and the mechanism involved in +1 PRF remain poorly understood. Previous study confirmed that +1 PRF is required for the synthesis of protein products in several genes of ciliates from the genus Euplotes. To accurately assess the frequency of genes requiring frameshift in Euplotes, the macronuclear genome and transcriptome of Euplotes octocarinatus were analyzed in this study. A total of 3,700 +1 PRF candidate genes were identified from 32,353 transcripts and the gene products of these putative +1 PRFs were mainly identified as protein kinases. Furthermore, we reported a putative suppressor tRNA of UAA which may provide new insights into the mechanism of +1 PRF in euplotids. For the first time, our transcriptome-wide survey of +1 PRF in E. octocarinatus provided a dataset which serves as a valuable resource for the future understanding of the mechanism underlying +1 PRF.