Histoplasma capsulatum produces an extracellular catalase termed M antigen, which is similar to catalase B of Aspergillus and Emericella species. Evidence is presented here for two additional catalase isozymes in H. capsulatum. Catalase A is highly similar to a large-subunit catalase in Aspergillus and Emericella species, while catalase P is a small-subunit catalase protein with greatest similarity to known peroxisomal catalases of animals and Saccharomycotina yeasts. Complete cDNAs for the CATA and CATP genes (encoding catalases A and P, respectively) were isolated. The transcriptional expression of the H. capsulatum CATA, CATB (M antigen) and CATP genes was assessed by Northern blot hybridizations on total RNA. Results at the transcript levels for these genes are shown for three conditions : cell morphology (mycelial versus yeast phase cells), oxidative stress (in response to a challenge with H 2 O 2 ) and carbon source (glucose vs glycerol). Collectively, these results demonstrated regulation of CATA by both cell morphology and oxidative stress, but not by carbon source, and regulation of CATB and CATP by carbon source but not cell morphology or oxidative stress. A phylogenetic analysis of presently available catalase sequences and intron residences was done. The results support a model for evolution of eukaryotic monofunctional catalase genes from prokaryotic genes.

We have sequenced and characterized the complete psbB gene cluster of Chlamydomonas reinhardtii chloroplast DNA. Although the petB and petD genes are located elsewhere, the sequential order of psbB, ORF31, psbN and psbH is identical to that of the psbB operon in higher plants. Also, intergenic non-coding regions are much larger in the Chlamydomonas gene cluster. Northern blot analyses indicate the formation of dicistronic transcripts of psbB and ORF31 and monocistronic transcripts of psbN and psbH. It is unclear whether a psbB operon is transcribed to yield a large polycistronic precursor but northern blot analysis with total RNA from cells grown at 15 degrees C does not detect an increased complexity of the transcripts, as has been found in studies of the psbB operon of higher plants. From primer extension and nuclease protection assays, it is apparent that 5' and 3' processing of the primary psbH transcript results in the accumulation of a heterogenous population of mRNAs. Northern blot analyses reveal transcription of Chlamydomonas psbN and show that its mRNA is much larger than that identified in liverwort and pea. The sequence identities of the PSII-H and PSII-N polypeptides as compared to their vascular plant counterparts is 50 to 62%. While the amino acid sequences of PSII-H and PSII-N proteins are significantly conserved, the mass of PSII-H from Chlamydomonas is significantly larger.

Previous investigators have reported the presence of two dominant proteins, tectonin I (25 kDa) and tectonin II (39 kDa), in nuclei and nuclear matrix from plasmodia of Physarum polycephalum. We demonstrate, by a modification of the nuclear isolation protocol and by protease sensitivity, that the tectonins are not nuclear proteins but rather are located on the exterior surface of the plasma membrane.We report the sequences of cDNAs of tectonins I and II, which encode 217 and 353 amino acids, respectively. Tectonin I is homologous to the C-terminal two-thirds of tectonin II. Both proteins contain six tandem repeats that are each 33-37 amino acids in length and define a new consensus sequence. Homologous repeats are found in L-6, a bacterial lipopolysaccharide-binding lectin from horseshoe crab hemocytes. The repetitive sequences of the tectonins and L-6 are reminiscent of the WD repeats of the ␤-subunit of G proteins, suggesting that they form ␤-propeller domains. Tectonin II has an additional N-terminal domain that includes a 47-residue sequence highly similar to the galactoside-binding sequence of the B-chain of ricin. The tectonins may be lectins that function as part of a transmembrane signaling complex during phagocytosis.In its plasmodial form, the myxomycete Physarum polycephalum exists as a multinucleated syncytium that feeds on bacteria and organic detritus by phagocytosis. The many nuclei within a single plasmodium progress through the cell cycle synchronously, and at the end of the G 2 phase undergo closed mitosis. Because of these characteristics, several investigators have examined the P. polycephalum nuclear matrix (1-4) and reported that, as with mammalian nuclear matrix, the P. polycephalum matrix contained a number of proteins ranging from approximately 40 kDa to more than 100 kDa but that it differed from mammalian nuclear matrix by having two dominant proteins with reported molecular masses of 23-28 and 35-38 kDa as determined by SDS-PAGE.1 The same proteins have also been found associated with purified rDNA chromatin (5). We have termed these proteins tectonins I and II, respectively.In the present study we report the cloning and sequencing of the cDNAs for the tectonins, and we use trypsin digestion of cell fractions to assess their localization in the plasmodium. We find that the tectonins are not nuclear proteins but instead are located on the plasmodial surface, and we report a method for purifying P. polycephalum nuclei not contaminated with the tectonins.The tectonins share with lectin L-6 of horseshoe crab hemocytes (6) six repeats of a novel consensus sequence that may form a ␤-propeller structure. Additionally, tectonin II contains in its N-terminal region a sequence similar to the galactosebinding domain of the B-chain of the plant toxin ricin (7). The tectonins may share with lectin L-6 the ability to recognize the outer membrane lipopolysaccharide of Gram-negative bacteria for phagocytosis and utilize an additional affinity for galactose to expand the number of ligands that they re...