The entire genomic RNA of a Spanish isolate of pepper mild mottle virus (PMMV-S), a resistance-breaking virus in pepper, was cloned and sequenced and shown to be similar to other tobamoviruses in its genomic organization. It consisted of 6357 nucleotides (nt) and contained four open reading frames (ORFs) which encode a 126K protein and a readthrough 183K protein (nt 70 to 4908), a 28K protein (nt 4909 to 5682) and a 17.5K coat protein (nt 5685 to 6158). This is the first tobamovirus in which none of the ORFs overlap. Both its nucleic acid and predicted protein sequences were compared with the previously determined sequences of other tobamoviruses. The variations and similarities found and their relationship with the pathogenicity of this virus are discussed.

The binding of N-acetyl-L-glutamate, the physiological allosteric activator, to rat liver carbamoyl-phosphate synthetase (ammonia) was studied by techniques of rate of dialysis and of ultracentrifugation in the Airfuge. There is one binding site for acetylglutamate per enzyme monomer ( M , 165 000). K ', Mg2 + (free) and ATP were required to demonstrate binding. The concentrations of ATP required indicate that binding of ATPA (the ATP molecule that yields Pi) is needed. HCO; was not essential, but it enhanced binding of acetylglutamate. Glycerol also favored binding. Plots of Kd values versus the reciprocal of free Mg2+ and ATP concentrations are linear and indicate that ATPA, K f and Mg2+ bind before acetylglutamate. In the presence of these ligands and HCOY, ammonia increased drastically the Kd value for acetylglutamate, whereas in absence of HCO; ammonia had little effect. This suggests that acetylglutamate dissociates with the products and explains the higher K , for acetylglutamate in the synthetase (overall) reaction than in the ATPase (partial) reaction. In the absence of ATP acetylglutamate was bound with high affinity if ADP and carbamoyl phosphate were present. A D P or carbamoyl phosphate alone did not promote substantial binding.Binding of acetylglutamate at low concentration was slow; it was accelerated at higher concentrations of the activator. Exchange of bound acetylglutamate with acetylglutamate in solution was fast.A scheme proposed earlier for allosteric activation of the enzyme [Rubio, V., Britton, H. G. and Grisolia, S. N-Acetyl-L-glutamate activates the mitochondria1 carbarnoyl-phosphate synthetase from ureotelic animals. This activator appears to play a key role in regulating the rate of carbamoyl phosphate production and thus of urea synthesis [I 1. Although the need for acetylglutamate was recognized early [2], its exact role has remained unclear for many years. Tests to demonstrate a direct participation of acetylglutamate in the reaction have always been negative. On the basis of this and of other indirect evidence it was suggested that acetylglutamate plays an allosteric role [3]. We provided strong support for this view by demonstrating that several cryoprotectants, unrelated to acetylglutamate, partly replace this agent [4]. As expected from an allosteric mechanism of activation, we also found enzyme activity in the absence of acetylglutamate and of cryoprotectants, and we compared the kinetics of the reaction in the absence and in the presence of acetylglutamate. From these and other results we have proposed a model for allosteric activation of the enzyme [5].To understand better the mode of action of acetylglutamate, information on binding of this cofactor would be

During a four‐year (1982–1985) survey of plant viruses infecting pepper cultivars grown under plastic in the Southeastern region of Spain, a tobamovirus was found to be the major disease agent of this crop. The virus produces slight or no symptoms on the leaves, but causes chlorotic mottling, malformation and reduction in size with occasional necrosis on the fruits and was able to infect all commercial pepper cultivars tested, including those resistant to other tobamoviruses, causing a catastrophic disease. The biological and serological characterization of the virus showed that it is very similar to pepper mild mottle virus (PMMV) (Wetteret al. 1984) and therefore we have termed it as Spanish strain of PMMV (PMMV‐S). The need of grouping all the so‐called “pepper strains” of tobacco mosaic virus (TMV) as a new distinct member of the tobamovirus group with the name of PMMV is emphasized.

A Spanish strain of pepper mild mottle virus (PMMV‐S) (Alonsoet al. 1989) can be differentiated from the Italian PMMV (Wetteret al. 1984) by the responses of Capsicum spp. with resistance genes to tobamoviruses, by radioimmunoassay and by the electrophoretic mobility of their viral particles. Moreover, the analysis of the electrophoretic mobility of the viral particles in agarose gels and that of the viral coat proteins in polyacrylamide‐urea gels are reliable and rapid techniques for distinguishing PMMV isolates from other members of the tobamovirus group and thus can be used for diagnostic purposes. These results support the proposal of grouping these pepper viruses, including the “pepper strains” of TMV, as a new tobamovirus subgroup (PARES 1985, BETTI et al. 1987, WETTER et al. 1987, ALONSO et al. 1989).