“…passages following cloning (Reichmann, Pringle & Follett, 197I ;Stampfer, Baltimore & Huang, 1971 ;Perrault & Holland, i972a;Holland, Villarreal & Breindl, I976a). These shorter truncated or T particles contain deleted forms of the genome or B RNA (Huang & Wagner, 1966;Brown et al 1967;Schaffer, Hackett & Soergel, 1968;Roy & Bishop, 1972) which specifically inhibit the replication of the latter (Huang & Manders,I972;Perrault & Holland,I972b).…”