mRNAcycling sequencebinding protein fromLeishmania donovani (LdCSBP) is covalentlymodi¢edbyubiquitination

The lack of transcriptional regulation in trypanosomatids suggests the presence of distinct posttranscriptional mechanisms to control differential gene expression. In fact, the stability of S-phase specific mRNAs in these parasites is determined primarily by the presence of the octanucleotide sequence (C/A)AUAGAA(G/A) in the UTRs of the transcripts. Here, the characterization of LdCSBP is reported, which specifically binds to the octanucleotide containing RNA. The LdCSBP protein contains multiple putative functional domains, including two types of ubiquitin binding domains (UBA and CUE), two CCCH-type Zn-finger motifs probably responsible for specific RNA binding activity and a speculative endonuclease domain SMR. Interestingly, the protein is covalently modified through ubiquitination. This observation and the occurrence of multiple ubiquitin binding domains in the protein raise the possibility of regulation of the activity of LdCSBP by ubiquitination.