In the generation of flavivirus particles, an internal cleavage of the envelope glycoprotein prM by furin is required for the acquisition of infectivity. Unlike cleavage of the prM of other flaviviruses, cleavage of dengue virus prM is incomplete in many cell lines; the partial cleavage reflects the influence of residues at furin nonconsensus positions of the pr-M junction, as flaviviruses share basic residues at positions P1, P2, and P4, recognized by furin. In this study, viruses harboring the alanine-scanning and other multiple-point mutations of the pr-M junction were generated, employing a dengue virus background that exhibited 60 to 70% prM cleavage and a preponderance of virion-sized extracellular particles. Analysis of prM and its cleavage products in viable mutants revealed a cleavage-suppressive effect at the conserved P3 Glu residue, as well as the cleavage-augmenting effects at the P5 Arg and P6 His residues, indicating an interplay between opposing modulatory influences mediated by these residues on the cleavage of the pr-M junction. Changes in the prM cleavage level were associated with altered proportions of extracellular virions and subviral particles; mutants with reduced cleavage were enriched with subviral particles and prM-containing virions, whereas the mutant with enhanced cleavage was deprived of these particles. Alterations of virus multiplication were detected in mutants with reduced prM cleavage and were correlated with their low specific infectivities. These findings define the functional roles of charged residues located adjacent to the furin consensus sequence in the cleavage of dengue virus prM and provide plausible mechanisms by which the reduction in the pr-M junction cleavability may affect virus replication.Dengue viruses are members of the genus Flavivirus in the family Flaviviridae. A single-stranded genomic RNA of positive polarity encodes an open reading frame which is translated into a precursor of three structural proteins and at least seven nonstructural proteins (27). During the replication of flaviviruses, proteolytic cleavages of the polyprotein by viral protease and a number of cellular enzymes occur in distinct subcellular compartments (27,32). Three structural proteins, C, prM/M, and E, are associated with the membrane of the rough endoplasmic reticulum (ER) by C-terminal membrane-spanning regions. Cleavages distal to the membrane-spanning regions of C and the two envelope glycoproteins prM and E by host signalase in the lumen of the rough ER and a cleavage proximal to the membrane-spanning region of C by viral protease in the cytoplasm are important to the assembly of viral particles (32). During the export of immature particles through the secretory pathway, cleavage of prM by the trans-Golgi apparatus resident furin allows reorganization of the receptor-binding E protein that is required for the acquisition of infectivity (9, 43).Assembly of flavivirus particles in the rough ER results in two types of particles: virions and subviral particles (32,40). An immature...