Identificationof the putative "Ciliary Localization Signal" in the axonemal beta-tubulin of Tetrahymena thermophila

Ciliogenesis relies on interflagellar transport (IFT) to move tubulin heterodimers, axonenemal molecular motors and other associated proteins, from the site of syntesis in the cell body to the site of function in the cilium. Beside the molecular mechanism of IFT are poorly understood, it has been found that the two core IFT proteins, IFT74 and IFT(!, have a role in the transport of tubulin alog the cilium (Bhogaraju et al,Science,2013). Howover, the putative signals involved in the incorporation of tubulin heterodimers into the axoneme have not been characterized.In the ciliated protozoa Tetrahymena thermophile, beta.tubulin is represented by two identical isotypes named BTU1 abd BTU2, which are most conserved and known as culinary tubulins, and six more divergent beta- tubulins, named beta-like (BLTs) and numbered from 1 to 6. We previously demonstrated (pucciarelli et al., Plosone, 2012) that two BLTs the BLT1 and BLT4, were not detectable in somatic meiotic apparatus of the nuclei. In contrast the BTU2 was detected mainly in cilia. These results suggest that cilioa and nuclei must recognize specific “key signal” to ensure the accurate targeting to and retention of proteins whithin these compartments. Here we propose a putative Ciliary Localization Signal (CLS) identified on the sequences of T. thermophile BTU2, which is responsible for the axonemal localization of this tubulin isotype.