A potent transrepression domain in the retinoblastoma protein induces a cell cycle arrest when bound to E2F sites.

An intact T/E1A-binding domain (the pocket) is necessary, but not sufficient, for the retinoblastoma protein (RB) to bind to DNA-protein complexes containing E2F and for RB to induce a G1/S block. Indirect evidence suggests that the binding of RB to E2F may, in addition to inhibiting E2F transactivation function, generate a complex capable of functioning as a transrepressor. Here we show that a chimera in which the E2F1 transactivation domain was replaced with the RB pocket could, in a DNA-binding and pocket-dependent manner, mimic the ability of RB to repress transcription and induce a cell cycle arrest. In contrast, a transdominant negative E2F1 mutant that is capable of blocking E2F-dependent transactivation did not. Fusion of the RB pocket to a heterologous DNA-binding domain unrelated to E2F likewise generated a transrepressor protein when scored against a suitable reporter. These results suggest that growth suppression by RB is due, at least in part, to transrepression mediated by the pocket domain bound to certain promoters via E2F.

Listeria monocytogenes empyema and bacteremia complicating chronic lymphocytic leukemia.

A 60-year-old man receiving corticosteroid and cyclophosphamide therapy for chronic lymphocytic leukemia developed an empyema and bacteremia due to Listeria monocytogenes. The rapidly fulminant course of Listeria infections in immunosuppressed hosts and the necessity of prompt treatment of Listeria empyemas are emphasized.

Properties of ion-bombarded fused quartz for integrated optics.

Development of techniques for production of carefully controlled, low-loss optical waveguides in solid dielectric materials is essential to development of integrated optical circuits for signal processing in future optical communications systems. Ion implantation offers an attractive possibility because of the refractive index and film thickness control possible by this technique. To evaluate this possibility we have investigated some of the optical properties of ion-bombarded fused quartz. A variety of ions ranging from helium ions to bismuth ions has been used. We have concentrated on refractive index and optical loss variations (on those implants into which a beam could be launched) as effected by (1) ion species and dose, (2) surface preparation, (3) surface temperature during bombardment, and (4) postbombardment annealing. This paper does not attempt to give an inclusive account of all the results obtained but principally discusses the best results so far, which are those using lithium ions. For lithium ion bombardment we have observed approximately linear variation of refractive index at 6328 A with dose n = n(0) + 2.1 x 10(-21)C, where n(0) is the prebombardment value (= 1.458 for fused quartz), and C is the ion concentration in ions/cm(3) (C < 2.2 x 10(19)). The optical absorption decreases significantly with increase in substrate temperature during implantation, and losses less than 0.2 dB/cm have been achieved. The refractive index change appears to be primarily due to disorder produced by the incident particles rather than a chemical doping effect as evidenced by postbombardment annealing studies.