Demethylation of trimethylated histone H3 Lys4 in vivo by JARID1 JmjC proteins

Histone H3 Lys4 trimethylation (H3-K4me3) is a conserved mark of actively transcribed chromatin. Using a conditional mutant of the yeast H3-K4 methyltransferase, Set1p, we demonstrate rapid turnover of H3-K4me3 and H3-K4me2 in vivo and show this process requires Yjr119Cp, of the JARID1 family of JmjC proteins. Ectopic overexpression of mouse Jarid1B, a Yjr119Cp homolog, greatly diminished H3-K4me3 and H3-K4me2 in HeLa cells, suggesting these proteins function as K4 demethylases in vivo.

Phase-variable expression of a family of glycoproteins imparts a dynamic surface to a symbiont in its human intestinal ecosystem

The recent report of the synthesis of glycoproteins by the abundant intestinal symbionts Bacteroides showed that these organisms use a novel bacterial enzyme to decorate their surfaces with a sugar residue derived from their environment. As a first step in understanding the importance of these glycoproteins to the bacteria and to the bacterial-host symbiosis, we identified and characterized the abundant glycoproteins of Bacteroides distasonis (proposed reclassification as Parabacteroides distasonis) [Sakamoto M, Benno Y (2006) Int J Syst Evol Microbiol 56:1599-1605]. Using lectin-affinity purification followed by tandem mass spectrometry, we identified a family of at least nine glycoproteins, similar only to the S-layer glycoproteins of Tannerella forsythia. Analysis of one of these purified glycoproteins demonstrated that the glycan is primarily a polymer of xylose, a monosaccharide rarely found in bacterial glycans. Even more unexpected was the finding that seven of nine of the glycoprotein promoters undergo DNA inversion, a process that we show is active in their endogenous human environment. Using cross-species functional assays, we show that a single serine family site-specific recombinase globally mediates the inversions of these glycoprotein promoters. This regulatory mechanism is similar to that of the Bacteroides fragilis capsular polysaccharides and establishes DNA inversion as a general and ancient means of regulation of glycan-containing surface molecules of these important human intestinal symbionts.

The role of Rat1 in coupling mRNA 3'-end processing to transcription termination: implications for a unified allosteric-torpedo model

The torpedo model of transcription termination by RNA polymerase II proposes that a 5'-3' RNA exonuclease enters at the poly(A) cleavage site, degrades the nascent RNA, and eventually displaces polymerase from the DNA. Cotranscriptional degradation of nascent RNA has not been directly demonstrated, however. Here we report that two exonucleases, Rat1 and Xrn1, both contribute to cotranscriptional degradation of nascent RNA, but this degradation is not sufficient to cause polymerase release. Unexpectedly, Rat1 functions in both 3'-end processing and termination by enhancing recruitment of 3'-end processing factors, including Pcf11 and Rna15. In addition, the cleavage factor Pcf11 reciprocally aids in recruitment of Rat1 to the elongation complex. Our results suggest a unified allosteric/torpedo model in which Rat1 is not a dedicated termination factor, but is an integrated component of the cleavage/polyadenylation apparatus.

Splicing speckles are not reservoirs of RNA polymerase II, but contain an inactive form, phosphorylated on serine2 residues of the C-terminal domain

"Splicing speckles" are major nuclear domains rich in components of the splicing machinery and polyA(+) RNA. Although speckles contain little detectable transcriptional activity, they are found preferentially associated with specific mRNA-coding genes and gene-rich R bands, and they accumulate some unspliced pre-mRNAs. RNA polymerase II transcribes mRNAs and is required for splicing, with some reports suggesting that the inactive complexes are stored in splicing speckles. Using ultrathin cryosections to improve optical resolution and preserve nuclear structure, we find that all forms of polymerase II are present, but not enriched, within speckles. Inhibition of polymerase activity shows that speckles do not act as major storage sites for inactive polymerase II complexes but that they contain a stable pool of polymerase II phosphorylated on serine(2) residues of the C-terminal domain, which is transcriptionally inactive and may have roles in spliceosome assembly or posttranscriptional splicing of pre-mRNAs. Paraspeckle domains lie adjacent to speckles, but little is known about their protein content or putative roles in the expression of the speckle-associated genes. We find that paraspeckles are transcriptionally inactive but contain polymerase II, which remains stably associated upon transcriptional inhibition, when paraspeckles reorganize around nucleoli in the form of caps.

RNA editing and alternative splicing: the importance of co-transcriptional coordination

The carboxy-terminal domain (CTD) of the large subunit of RNA polymerase II (pol II) is essential for several co-transcriptional pre-messenger RNA processing events, including capping, 3'-end processing and splicing. We investigated the role of the CTD of RNA pol II in the coordination of A to I editing and splicing of the ADAR2 (ADAR: adenosine deaminases that act on RNA) pre-mRNA. The auto-editing of Adar2 intron 4 by the ADAR2 adenosine deaminase is tightly coupled to splicing, as the modification of the dinucleotide AA to AI creates a new 3' splice site. Unlike other introns, the CTD is not required for efficient splicing of intron 4 at either the normal 3' splice site or the alternative site created by editing. However, the CTD is required for efficient co-transcriptional auto-editing of ADAR2 intron 4. Our results implicate the CTD in site-selective RNA editing by ADAR2 and in coordination of editing with alternative splicing.

Ribozyme cleavage reveals connections between mRNA release from the site of transcription and pre-mRNA processing

We report a functional connection between splicing and transcript release from the DNA. A Pol II CTD mutant inhibited not only splicing but also RNA release from the site of transcription. A ribozyme situated downstream of the gene restored accurate splicing inhibited by the CTD mutant or a mutant poly(A) site, suggesting that cleavage liberates RNA from a niche that is inaccessible to splicing factors. Although ribozyme cleavage enhanced splicing, 3' end processing was impaired, indicating that an intact RNA chain linking the poly(A) site to Pol II is required for optimal processing. Surprisingly, poly(A)(-) beta-globin mRNA with a ribozyme-generated 3' end was exported to the cytoplasm. Ribozyme cleavage can therefore substitute for normal 3' end processing in stimulating splicing and mRNA export. We propose that mRNA biogenesis is coordinated by preventing splicing near the 3' end until the transcript is released by poly(A) site cleavage.

Rules of engagement: co-transcriptional recruitment of pre-mRNA processing factors

The universal pre-mRNA processing events of 5' end capping, splicing, and 3' end formation by cleavage/polyadenylation occur co-transcriptionally. As a result, the substrate for mRNA processing factors is a nascent RNA chain that is being extruded from the RNA polymerase II exit channel at 10-30 bases per second. How do processing factors find their substrate RNAs and complete most mRNA maturation before transcription is finished? Recent studies suggest that this task is facilitated by a combination of protein-RNA and protein-protein interactions within a 'mRNA factory' that comprises the elongating RNA polymerase and associated processing factors. This 'factory' undergoes dynamic changes in composition as it traverses a gene and provides the setting for regulatory interactions that couple processing to transcriptional elongation and termination.

Altered nucleosome occupancy and histone H3K4 methylation in response to 'transcriptional stress'

We report that under 'transcriptional stress' in budding yeast, when most pol II activity is acutely inhibited, rapid deposition of nucleosomes occurs within genes, particularly at 3' positions. Whereas histone H3K4 trimethylation normally marks 5' ends of highly transcribed genes, under 'transcriptional stress' induced by 6-azauracil (6-AU) and inactivation of pol II, TFIIE or CTD kinases Kin28 and Ctk1, this mark shifted to the 3' end of the TEF1 gene. H3K4Me3 at 3' positions was dynamic and could be rapidly removed when transcription recovered. Set1 and Chd1 are required for H3K4 trimethylation at 3' positions when transcription is inhibited by 6-AU. Furthermore, Deltachd1 suppressed the growth defect of Deltaset1. We suggest that a 'transcriptional stress' signal sensed through Set1, Chd1, and possibly other factors, causes H3K4 hypermethylation of newly deposited nucleosomes at downstream positions within a gene. This response identifies a new role for H3K4 trimethylation at the 3' end of the gene, as a chromatin mark associated with impaired pol II transcription.

RNA polymerase II carboxy-terminal domain phosphorylation is required for cotranscriptional pre-mRNA splicing and 3'-end formation

We investigated the role of RNA polymerase II (pol II) carboxy-terminal domain (CTD) phosphorylation in pre-mRNA processing coupled and uncoupled from transcription in Xenopus oocytes. Inhibition of CTD phosphorylation by the kinase inhibitors 5,6-dichloro-1beta-D-ribofuranosyl-benzimidazole and H8 blocked transcription-coupled splicing and poly(A) site cleavage. These experiments suggest that pol II CTD phosphorylation is required for efficient pre-mRNA splicing and 3'-end formation in vivo. In contrast, processing of injected pre-mRNA was unaffected by either kinase inhibitors or alpha-amanitin-induced depletion of pol II. pol II therefore does not appear to participate directly in posttranscriptional processing, at least in frog oocytes. Together these experiments show that the influence of the phosphorylated CTD on pre-mRNA splicing and 3'-end processing is mediated by transcriptional coupling.

The link between mRNA processing and transcription: communication works both ways

Many pre-mRNA processing events including 5' end capping, splicing out introns, and 3' end maturation by cleavage or polyadenylation occur while the nascent RNA chain is being synthesized by RNA polymerase II. As a consequence of this arrangement, the physiological substrate for most processing factors is not a solitary pre-RNA but instead a ternary complex comprising a growing RNA chain spewing from the exit channel of an RNA polymerase II molecule as it speeds along a chromatin template at 1000-2000 bases/min. mRNA processing factors make protein-protein contacts with elongating pol II in a complex we have dubbed the "mRNA factory," which carries out synthesis, processing, and packaging of the transcript. Recent studies have shown that the "mRNA factory" is a dynamic complex whose composition changes as it traverses the length of a gene. This complex is also the setting for a growing number of regulatory interactions, which influence the function of both the processing and transcription machineries.

A 10 residue motif at the C-terminus of the RNA pol II CTD is required for transcription, splicing and 3' end processing

The RNA polymerase II C-terminal heptad repeat domain (CTD) is essential for normal transcription and co-transcriptional processing of mRNA precursors. The mammalian CTD comprises 52 heptads whose consensus, YSPTSPS, is conserved throughout eukaryotes, followed by a 10 amino acid C-terminal sequence that is conserved only among vertebrates. Here we show that surprisingly, the heptad repeats are not sufficient to support efficient transcription, pre-mRNA processing or full cell viability. In addition to the heptads, the 10 amino acid C-terminal motif is essential for high level transcription, splicing and poly(A) site cleavage. Efficient mRNA synthesis from a transiently transfected reporter gene required the C-terminal motif plus between 16 and 25 heptad repeats from either the N- or C-terminal half of the CTD. Twenty-seven consensus heptads plus the C-terminal motif also supported efficient mRNA synthesis but not cell viability.

The C-terminal domain of pol II and a DRB-sensitive kinase are required for 3' processing of U2 snRNA

The human snRNA genes transcribed by RNA polymerase II (e.g. U1 and U2) have a characteristic TATA-less promoter containing an essential proximal sequence element. Formation of the 3' end of these non-polyadenylated RNAs requires a specialized 3' box element whose function is promoter specific. Here we show that truncation of the C-terminal domain (CTD) of RNA polymerase II and treatment of cells with CTD kinase inhibitors, including DRB (5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole), causes a dramatic reduction in proper 3' end formation of U2 transcripts. Activation of 3' box recognition by the phosphorylated CTD would be consistent with the role of phospho-CTD in mRNA processing. CTD kinase inhibitors, however, have little effect on initiation or elongation of transcription of the U2 genes, whereas elongation of transcription of the beta-actin gene is severely affected. This result highlights differences in transcription of snRNA and mRNA genes.

Functional interaction of yeast pre-mRNA 3' end processing factors with RNA polymerase II

The RNA polymerase II CTD is essential for 3' end cleavage of metazoan pre-mRNAs and binds 3' end processing factors in vitro. We show genetic and biochemical interactions between the CTD and the Pcf11 subunit of the yeast cleavage/polyadenylation factor, CFIA. In vitro binding to Pcf11 required phosphorylation of the CTD on Ser2 in the YSPTSPS heptad repeats. Deletion of the yeast CTD reduced the efficiency of cleavage at poly(A) sites, and the length of poly(A) tails suggesting that it helps couple 3' end formation with transcription. Consistent with this model, the 3' end processing factors CFIA, CFIB, and PFI were recruited to genes progressively, starting at the 5' end, in a process that required ongoing transcription.

Subcellular localization of NAD(P)H:quinone oxidoreductase 1 in human cancer cells

NAD(P)H:quinone oxidoreductase 1 (NQO1) is implicated in both chemoprevention and bioactivation of DNA-damaging antitumor agents. NQO1 is mainly cytosolic, but distribution in other cellular compartments, particularly in tumor cells, is poorly defined. Nuclear NQO1 in HT29 human colon carcinoma and H661 human non-small cell lung cancer cells was observed using both confocal microscopy and immunoelectron microscopy. NQO1 was not detected in mitochondria, golgi, or endoplasmic reticulum. In addition, purified intact nuclei from HT29 cells contained immunoreactive NQO1, which was catalytically active as determined by conventional activity assay. In summary, we have confirmed the presence of nuclear NQO1, which has implications for chemoprotection and bioactivation of DNA-damaging antitumor agents.

Assessment of white matter injury following prolonged focal cerebral ischaemia in the rat

The ability of putative neuroprotective compounds to protect against white matter injury remains poorly investigated due to the lack of suitable methods for assessing white matter injury. This study was therefore designed to investigate the utility of Tau 1 (oligodendrocytes/axons), myelin basic protein (MBP; myelin) and amyloid precursor protein (APP; axons) immunohistochemistry in assessing white matter injury at various times following middle cerebral artery occlusion (MCAO) in the rat. Focal cerebral, ischaemia was induced in halothane-anaesthetised rats using an intraluminal thread model. At 24 h, 1 and 2 weeks following MCAO, white matter injury was assessed using Tau 1, APP, MBP and Luxol-fast blue staining and neuronal injury with cresyl fast violet (CFV). In histologically normal tissue MBP immunoreactivity was detected in myelinated fibre tracts, while Tau 1 and APP were axonally located. At 24 h following permanent MCAO, MBP, and Tau 1 staining remained relatively unchanged within the myelin and axonal compartments of the ischaemic region. In contrast, increased Tau 1 staining was apparent in oligodendrocytes within ischaemic tissue, while APP accumulated in axons surrounding the lesion. At 1 and 2 weeks following transient MCAO, Tau 1 and APP staining was markedly decreased within ischaemic tissue. Marked reduction in MBP levels within ischaemic tissue were not detected until 2 weeks following MCAO. The area of axonal injury as assessed by reduced Tau 1 or APP staining correlated with the area of neuronal damage as assessed by CFV staining. This study shows that MBP, Tau 1 and APP immunohistochemistry can be utilised to assess myelin and axonal integrity following sustained ischaemia using standard image analysis techniques.

Capping, splicing, and 3' processing are independently stimulated by RNA polymerase II: different functions for different segments of the CTD

Capping, splicing, and cleavage/polyadenylation of pre-mRNAs are interdependent events that are all stimulated in vivo by the carboxy-terminal domain (CTD) of RNA Pol II. We show that the CTD independently enhances splicing and 3' processing and that stimulation of splicing by enhancers is facilitated by the CTD. We provide evidence that stimulation of 3' processing by the CTD requires contact with the 50-kD subunit of the cleavage stimulation factor, CstF. Overexpression of the CTD-binding domain of CstF p50 had a dominant-negative effect on 3' processing without disrupting the CstF complex. The CTD comprises 52 heptad repeats. The CTD carboxyl terminus including heptads 27-52 supported capping, splicing, and 3' processing but the amino terminus supported only capping. We conclude that the CTD independently stimulates all three major pre-mRNA processing steps and that different regions of the CTD can serve distinct functions in pre-mRNA processing.

Transcription elongation: the 'Foggy' is liftingellipsis

Transcription can be controlled by regulating either the initiation or elongation of RNA chains. Recent studies highlight the importance of an elongation regulator, Spt5, in controlling gene expression in yeast, fruit fly and zebrafish; Spt5 may provide a link between transcriptional elongation and cell fate.

MCM proteins are associated with RNA polymerase II holoenzyme

MCMs are a family of proteins related to ATP-dependent helicases that bind to origin recognition complexes and are required for initiation of DNA replication. We report that antibodies against MCM2(BM28) specifically inhibited transcription by RNA polymerase II (Pol II) in microinjected Xenopus oocytes. Consistent with this observation, MCM2 and other MCMs copurified with Pol II and general transcription factors (GTFs) in high-molecular-weight holoenzyme complexes isolated from Xenopus oocytes and HeLa cells. Pol II and GTFs also copurified with MCMs isolated by anti-MCM3 immunoaffinity chromatography. MCMs were specifically displaced from the holoenzyme complex by antibody against the C-terminal domain (CTD) of Pol II. In addition, MCMs bound to a CTD affinity column, suggesting that their association with holoenzyme depends in part on this domain of Pol II. These results suggest a new function for MCM proteins as components of the Pol II transcriptional apparatus.

Optimization of capillary chromatography ion trap-mass spectrometry for identification of gel-separated proteins

The current paradigm for protein identification using mass spectrometric derived peptide-mass and fragment-ion data employs computer algorithms which match uninterpreted or partially interpreted fragment-ion data to sequence databases, both protein and translated nucleotide sequence databases. Nucleotide sequence databases continue to grow at a rapid rate for some species, providing an unsurpassed resource for protein identification in those species. Ion-trap mass spectrometers with their ability to rapidly generate fragment-ion spectra in a data-dependent manner with high sensitivity and accuracy has led to their increased use for protein identification. We have investigated various parameters on a commercial ion trap-mass spectrometer to enhance our ability to identify peptides separated by capillary reversed phase-high performance liquid chromatography (RP-HPLC) coupled on-line to the mass spectrometer. By systematically evaluating the standard parameters (ion injection time and number of microscans) together with selection of multiple ions from the full mass range, improved tandem mass spectrometry (MS/MS) spectra were generated, facilitating identification of proteins at a low pmol level. Application of this technology to the identification of a standard protein and an unknown from an affinity-enriched mixture are shown.

Optimization of capillary chromatography ion trap-mass spectrometry for identification of gel-separated proteins

The current paradigm for protein identification using mass spectrometric derived peptide-mass and fragment-ion data employs computer algorithms which match uninterpreted or partially interpreted fragment-ion data to sequence databases, both protein and translated nucleotide sequence databases. Nucleotide sequence databases continue to grow at a rapid rate for some species, providing an unsurpassed resource for protein identification in those species. Ion-trap mass spectrometers with their ability to rapidly generate fragment-ion spectra in a data-dependent manner with high sensitivity and accuracy has led to their increased use for protein identification. We have investigated various parameters on a commercial ion trap-mass spectrometer to enhance our ability to identify peptides separated by capillary reversed phase-high performance liquid chromatography (RP-HPLC) coupled on-line to the mass spectrometer. By systematically evaluating the standard parameters (ion injection time and number of microscans) together with selection of multiple ions from the full mass range, improved tandem mass spectrometry (MS/MS) spectra were generated, facilitating identification of proteins at a low pmol level. Application of this technology to the identification of a standard protein and an unknown from an affinity-enriched mixture are shown.

5'-Capping enzymes are targeted to pre-mRNA by binding to the phosphorylated carboxy-terminal domain of RNA polymerase II

We have investigated the role of the RNA Polymerase II (Pol II) carboxy-terminal domain (CTD) in mRNA 5' capping. Transcripts made in vivo by Pol II with a truncated CTD had a lower proportion of capped 5' ends than those made by Pol II with a full-length CTD. In addition, the enzymes responsible for cap synthesis, RNA guanylyltransferase, and RNA (guanine-7)-methyltransferase bound directly to the phosphorylated, but not to the nonphosphorylated, form of the CTD in vitro. These results suggest that: (1) Pol II-specific capping of nascent transcripts in vivo is enhanced by recruitment of the capping enzymes to the CTD and (2) capping is co-ordinated with CTD phosphorylation.

Regulation of CDK7 substrate specificity by MAT1 and TFIIH

The cyclin-dependent kinase (CDK)-activating kinase CAK has been proposed to function in the control of cell cycle progression, DNA repair and RNA polymerase II (pol II) transcription. Most CAK exists as complexes of three subunits: CDK7, cyclin H (CycH) and MAT1. This tripartite CAK occurs in a free form and in association with 'core' TFIIH, which functions in both pol II transcription and DNA repair. We investigated the substrate specificities of different forms of CAK. Addition of the MAT1 subunit to recombinant bipartite CDK7-CycH switched its substrate preference to favour the pol II large subunit C-terminal domain (CTD) over CDK2. We suggest that the MAT1 protein, previously shown to function as an assembly factor for CDK7-CycH, also acts to modulate CAK substrate specificity. The substrate specificities of natural TFIIH and free CAK were also compared. TFIIH had a strong preference for the CTD over CDK2 relative to free CAK. TFIIH, but not free CAK, could efficiently hyperphosphorylate the CTD. In the context of TFIIH, the kinase also acquired specificity for the general transcription factors TFIIE and TFIIF which were not recognized by free CAK. We conclude that the substrate preference of the CDK7-CycH kinase is governed by association with both MAT1 and 'core' TFIIH.

Protective monoclonal antibody defines a circumsporozoite-like glycoprotein exoantigen of Cryptosporidium parvum sporozoites and merozoites

The apicomplexan protozoan parasite Cryptosporidium parvum causes a diarrheal disease in humans and other mammals for which specific therapy and immunoprophylaxis are unavailable. Passive immunization with Abs against whole C. parvum organisms has variable efficacy in immunocompromised or neonatal hosts. Because apical and surface-exposed zoite Ags of the Apicomplexa are critical to infectivity and targets of protective immunity, we examined the ability of mAbs generated against such Ags in C. parvum sporozoites to passively protect against infection and identify biologically relevant parasite molecules. A panel of mAbs was produced against affinity-purified native Ags using sporozoite apical- and surface-reactive mAb C4A1 as binding ligand. One resulting mAb, designated 3E2, elicited prominent morphologic changes in sporozoites and merozoites characterized by rapid and progressive formation, posterior movement, and release of membranous Ag-mAb precipitates. These changes had a striking resemblance to the malarial circumsporozoite precipitate (CSP) reaction. Sporozoite infectivity was completely neutralized after in vitro exposure to 3E2 and the CSP-like reaction. Furthermore, orally administered 3E2 completely prevented or markedly reduced infection in neonatal BALB/c mice. 3E2 bound to apical complex and surface molecules of zoites and was demonstrated in membranous precipitates by immunoelectron microscopy. In Western blots, 3E2 recognized multiple 46 to approximately 770 kDa sporozoite Ags and an approximately 1300-kDa Ag designated CSL, also expressed by merozoites. CSL was characterized as a soluble glycoprotein exoantigen released by infectious sporozoites. Further, CSL was determined to be the molecular species mechanistically involved in the CSP-like reaction by its identification in SDS-PAGE gels and Western blots of purified membranous precipitates. These findings indicate that CSL has a functional role in sporozoite infectivity and is a candidate molecular target for passive or active immunization against cryptosporidiosis.

Protective monoclonal antibody defines a circumsporozoite-like glycoprotein exoantigen of Cryptosporidium parvum sporozoites and merozoites

The apicomplexan protozoan parasite Cryptosporidium parvum causes a diarrheal disease in humans and other mammals for which specific therapy and immunoprophylaxis are unavailable. Passive immunization with Abs against whole C. parvum organisms has variable efficacy in immunocompromised or neonatal hosts. Because apical and surface-exposed zoite Ags of the Apicomplexa are critical to infectivity and targets of protective immunity, we examined the ability of mAbs generated against such Ags in C. parvum sporozoites to passively protect against infection and identify biologically relevant parasite molecules. A panel of mAbs was produced against affinity-purified native Ags using sporozoite apical- and surface-reactive mAb C4A1 as binding ligand. One resulting mAb, designated 3E2, elicited prominent morphologic changes in sporozoites and merozoites characterized by rapid and progressive formation, posterior movement, and release of membranous Ag-mAb precipitates. These changes had a striking resemblance to the malarial circumsporozoite precipitate (CSP) reaction. Sporozoite infectivity was completely neutralized after in vitro exposure to 3E2 and the CSP-like reaction. Furthermore, orally administered 3E2 completely prevented or markedly reduced infection in neonatal BALB/c mice. 3E2 bound to apical complex and surface molecules of zoites and was demonstrated in membranous precipitates by immunoelectron microscopy. In Western blots, 3E2 recognized multiple 46 to approximately 770 kDa sporozoite Ags and an approximately 1300-kDa Ag designated CSL, also expressed by merozoites. CSL was characterized as a soluble glycoprotein exoantigen released by infectious sporozoites. Further, CSL was determined to be the molecular species mechanistically involved in the CSP-like reaction by its identification in SDS-PAGE gels and Western blots of purified membranous precipitates. These findings indicate that CSL has a functional role in sporozoite infectivity and is a candidate molecular target for passive or active immunization against cryptosporidiosis.

The C-terminal domain of RNA polymerase II couples mRNA processing to transcription

Messenger RNA is produced by RNA polymerase II (pol II) transcription, followed by processing of the primary transcript. Transcription, splicing and cleavage-polyadenylation can occur independently in vitro, but we demonstrate here that these processes are intimately linked in vivo. We show that the carboxy-terminal domain (CTD) of the pol II large subunit is required for efficient RNA processing. Splicing, processing of the 3' end and termination of transcription downstream of the poly(A) site, are all inhibited by truncation of the CTD. We found that the cleavage-polyadenylation factors CPSF and CstF specifically bound to CTD affinity columns and copurified with pol II in a high-molecular-mass complex. Our demonstration of an association between the CTD and 3'-processing factors, considered together with reports of a similar interaction with splicing factors, suggests that an mRNA 'factory' exists which carries out coupled transcription, splicing and cleavage-polyadenylation of mRNA precursors.