GENE STRUCTURE AND SEQUENCE COMPARISONS OF THE EYE LENS SPECIFIC PROTEIN, FILENSIN, FROM RAT AND MOUSE - IMPLICATIONS FOR PROTEIN CLASSIFICATION AND ASSEMBLY

The full length cDNA sequences of rat and mouse filensin are presented , as well as the structure of the rat filensin gene. This gene spanned 31 kb and included seven introns. The first six introns were conserve d in position and phase with those found in the intermediate filament (IF) protein genes of the type II (type II keratin), type III (vimenti n) and type V (lamin). The last intron of the filensin was unique. As none of the filensin intron positions coincided with those unique to t ype I, II or IV genes, it appears that filensin is most similar to typ e III genes. Comparison of the deduced amino acid sequences for rat an d mouse filensin with those of cow and chick, and with other species o f IF proteins, indicated the C-terminal non-alpha-helical tail domain of filensin to be one of the most divergent yet found in the vertebrat e IF family. The tail domain had three conserved regions which are int errupted with two regions with lower identity. Two motifs, (1) PGDVPDG xxISKAF; and (2) KVEVVESIEKxxxxxIQTYEETxxIVET, were identified as sequ ences which were particularly highly conserved across species. Coassem bly studies using CP49 and a physiologically derived 53 kDa-fragment o f filensin showed the motif(2) was not required for filament assembly in vitro. These data strengthen the view that the C-terminal non-alpha -helical domain of filensin contributes in more than one way to filens in function in the lens. (C) 1997 Elsevier Science B.V.