Abstract. Using morphological and cell biological techniques, we have shown that the RNA replicase of Semliki Forest and Sindbis virus (two closely related alphaviruses) is located in complex ribonucleoprotein structures associated with the cytoplasmic surface of modified secondary lysosomes and endosomes. These nucleoprotein complexes often form a bridge between the membrane of the endocytic vacuole and the rough endoplasmic reticulum where the synthesis of the structural proteins of these viruses occurs. The results suggest that these cytopathic vacuoles constitute sites not only for viral RNA synthesis, but also for translation of structural proteins, and for the assembly of nucleocapsids.URINC the initial stages of virus infection, the genome and accessory proteins of incoming virions are delivered into the cytosol of the animal cell. Penetration into the cytosol occurs, as a rule, through the plasma membrane or the membrane of endocytic vacuoles. Subsequent uncoating of the genome and replication takes place either in the nucleus, in association with cytoplasmic organelles, or in soluble cytoplasmic complexes. In many cases cellular factors appear to be needed in the early cytosolic processes. While the mechanisms of penetration and the molecular events during replication are increasingly well understood for many viruses, little is now known about nucleocapsid uncoating, intracytoplasmic relocation, transport to the nucleus, and association with intracellular proteins and organelles.In this paper we address the cell biology of the early cytoplasmic events during Semliki Forest virus (SFV) ~ and Sindbis virus infection. These alphaviruses are known to enter cells by receptor-mediated endocytosis via coated pits, followed by acid-activated membrane fusion in the endosomal compartment (see . As a result the nucleocapsid, an isometric spherical particle composed of a single-stranded RNA molecule and 240 copies of a single capsid protein (Fuller, 1987), is released into the cytoplasm. The subsequent replication of alphaviral RNA occurs entirely within the cytoplasmic compartment in association with cytoplasmic organelles (see Strauss and Strauss, 1986).

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Quantitative structure-activity relationships have been found among macrolide antibacterial agents in their potencies against the bacterial pathogen Pasteurella multocida both in vitro and in mouse infections. To obtain these relationships we measured, among other things, the pK(a)'s and log P's of 15 known macrolides of diverse structures. Among these compounds, in vitro potency [log(1/MIC)] is a function of log P, log D, and CMR (R = 0.86). In vivo potency is a function of the higher pK(a), the HPLC chromatographic capacity factor log k', log(1/MIC) and pNF (R = 0.93). pNF is defined as the negative logarithm of the fraction of neutral drug molecules present in aqueous solution at pH 7.4. The same physical properties were determined for 14 macrolides not used in developing the original QSAR models. Using the in vivo model, we calculated the mouse protection potency ranges for these new compounds. Ten estimates agreed with those observed, three were lower by a half-order of magnitude, and one was calculated to be active in the range of 15-50 mg/kg, but in fact was not active at 50 mg/kg, the highest level tested. When these new compounds were combined with the original 15, and the QSAR's updated, the new equations for the in vitro and in vivo potencies were essentially the same as those originally found. Hence, the physical properties indicated above are major determinants of macrolide antibacterial potencies.

Danofloxacin (CP-76,136) is in a class of agents that inhibit DNA gyrase and trigger induction of the SOS response and temperate bacteriophages. Killing studies against the bovine pathogen Pasteurella haemolytica demonstrated that danofloxacin exhibits particularly rapid killing kinetics. Here, lysogenic Escherichia coli bearing lambda is found to be more sensitive to danofloxacin than nonlysogenic E. coli. Danofloxacin exposure also induced a prophage in P. haemolytica. The potency of danofloxacin against lysogens in likely enhanced by this prophage induction.

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