PROKARYOTIC HOMOLOG OF TUBULIN - CONSIDERATION OF FTSZ AND GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE AS PROBABLE CANDIDATES

The bacterial FtsZ protein has recently been suggested as a probable p rokaryotic homolog of the tubulin family of proteins (Cell 80, 1995, 3 67-370). We have compared the sequence similarity of tubulins to FtsZ and another protein glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Both these proteins exhibited similar levels of sequence identity to t he tubulins, which in a few cases was indicated to be significant. We report that incubation of the GAPDH in microtubule assembly buffer cau ses its polymerization into filamentous structures. In eukaryotic cell s, GAPDH is known to be associated with cytoskeletal structures and it binds specifically to both tubulins and colchicine. The latter is a d istinctive characteristic of the tubulin family of proteins. These obs ervations indicate that similar to the FtsZ proteins, GAPDH also exhib its a number of intriguing similarities to the tubulins. Whether any o f these proteins truly represent the prokaryotic homolog of tubulin, h owever, is unclear at present.