“…This excludes p94 fer from being de®ned as an ubiquitous tyrosine kinase. Since the expression of cFes is also restricted to de®ned tissues (MacDonald et al, 1985;Hanazono et al, 1993;Greer et al, 1990Greer et al, , 1994Feldman et al, 1985;Care et al, 1996), this leaves c-Abl as the only known, ubiquitous nuclear tyrosine kinase, which is expressed in all mammalian cells (Wang and Baltimore, 1983;Renshaw et al, 1988;Muller et al, 1982;Boulter and Wagner, 1988;Bernards et al, 1988). The absence of p94 fer from lymphoid progenitor cells and the proven presence of c-Fes in T (Izuhara et al, 1994) and p94 fer in B cell lines, apparently leaves the pre-T and pre-B cells as the only cells, known to harbor c-Abl (Wang and Baltimore, 1983;Renshaw et al, 1988;Ben-Neriah et al, 1986) and not c-Fes or p94 fer .…”