Molecular and functional organization of yeast plasmid pSR1.

The nucleotide sequence of a 6251 base-pair plasmid, pSR1, harbored in an osmophilic haploid yeast, Zygosaccharomyces rouxii (formerly Saccharomyces rouxii), was determined. No homology was detected between the sequences of pSR1 and 2-micron DNA of Saccharomyces cerevisiae. pSR1 has a pair of inverted repeats consisting of completely homologous 959 base-pair sequences, which separate two unique sequences 2654 base-pairs and 1679 base-pairs long. Each inverted repeat has an ARS sequence functional in both Z. rouxii and S. cerevisiae hosts. Short direct repeats or dyad symmetries were observed in the inverted repeats similar to those found close to the replication origin of 2-micron DNA. Three open reading frames, P, S and R, each able to encode a protein of molecular weight larger than 10,000, were found. Insertional inactivation of R gave rise to a defect in the intramolecular recombination at the inverted repeats, and that of S reduced the copy number of pSR1 in the S. cerevisiae host. The maintenance stability of the plasmid was also tested in the heterogeneous S. cerevisiae host, but the results of the insertional inactivation of P, S and R were ambiguous. pSR1 and 2-micron DNA were compatible in S. cerevisiae cells, but the protein factors encoded by these plasmids did not complement each other.

Molecular complexes of quinoline antimalarials with iron-porphyrin components of protease-digested methemoglobin.

Chloroquine, quinine, mefloquine and quinacrine have been found by difference spectroscopy to interact with hemozoin from Plasmodium berghei, trypsin and pronase-digested methemoglobin, hemin, heme, protoporphyrin IX and hematoporphyrin. These drugs also compete with one another in their binding to hemin. It is proposed that the iron-porphyrin moiety of digested hemoglobin is a common binding site for the accumulation of the schizontocidal drugs in the autophagosomes of the malarial parasite.

Binding of antimalarial drugs to hemozoin from Plasmodium berghei.

Chloroquine, quinacrine and mefloquine bind to Plasmodium berghei hemozoin, hemin, hemi, protoporphyrin IX and protease digested methemoglobin. This binding may be the basis for drug accumulation and action in the parasite.