Nucleocapsid protein 7 (NCp7), the human immunodeficiency virus type 1 (HIV-1) nucleocapsid protein, was shown to strongly potentiate the dimerization of the retroviral genomic RNA. This process involves the interaction of two retroviral RNA monomer subunits near their 5-ends. A region located upstream from the splice donor site was recently identified as being responsible for the formation of dimeric HIV-1 RNA. This region appeared to be confined within a stem-loop structure, with an autocomplementary sequence in the loop. In an in vitro study of spontaneous dimer formation, we reported that the 77-402 RNA transcript forms two distinct dimers differing in their thermostability: D37 and D55. We identified D37 as a "kissing" complex structure, formed via a loop-loop interaction between the two monomers, and D55 as a double stranded structure involving all nucleotides of the stem-loop via canonical base pairing. In this report, we have characterized the role of NCp7 in the HIV-1 Lai RNA dimerization process by using in vitro dimerization assays with RNA transcripts of different lengths and dimer thermal dissociation. Our results show that the nucleocapsid protein NCp7 activates RNA dimerization very likely through interaction with the kissing complex and converts it into a stable dimer. Furthermore, this NCp7-promoted conversion only occurs if the 240 -280 stem-loop structure is present in HIV-1 Lai RNA molecules and contains the autocomplementary G 257 CGCGC 262 sequence. This study suggests that, under physiological conditions, an NCp7-mediated RNA conformational change is involved in the maturation of the HIV-1 RNA dimer.

As a first step in the synthesis and the study of DNA polyintercalating drugs, dimers of acridines have been prepared. Their DNA binding properties have been studied. It has been determined that wen the chain separating the two aromatic rings is longer than a critical distance, bisintercalation is actually observed and that the DNA binding affinity becomes quite large (>108-109 M-1). It is shown also that the optical characteristics of these molecules are dependent on the sequences of DNA. The fluorescence intensity of one of these dimers when bound to DNA varies as the fourth power of its A+T content. This derivative could be used as a fluorescent probe of DNA sequence.