The DSIF Subunits Spt4 and Spt5 Have Distinct Roles at Various Phases of Immunoglobulin Class Switch Recombination

Class-switch recombination (CSR), induced by activation-induced cytidine deaminase (AID), can be divided into two phases: DNA cleavage of the switch (S) regions and the joining of the cleaved ends of the different S regions. Here, we show that the DSIF complex (Spt4 and Spt5), a transcription elongation factor, is required for CSR in a switch-proficient B cell line CH12F3-2A cells, and Spt4 and Spt5 carry out independent functions in CSR. While neither Spt4 nor Spt5 is required for transcription of S regions and AID, expression array analysis suggests that Spt4 and Spt5 regulate a distinct subset of transcripts in CH12F3-2A cells. Curiously, Spt4 is critically important in suppressing cryptic transcription initiating from the intronic Sμ region. Depletion of Spt5 reduced the H3K4me3 level and DNA cleavage at the Sα region, whereas Spt4 knockdown did not perturb the H3K4me3 status and S region cleavage. H3K4me3 modification level thus correlated well with the DNA breakage efficiency. Therefore we conclude that Spt5 plays a role similar to the histone chaperone FACT complex that regulates H3K4me3 modification and DNA cleavage in CSR. Since Spt4 is not involved in the DNA cleavage step, we suspected that Spt4 might be required for DNA repair in CSR. We examined whether Spt4 or Spt5 is essential in non-homologous end joining (NHEJ) and homologous recombination (HR) as CSR utilizes general repair pathways. Both Spt4 and Spt5 are required for NHEJ and HR as determined by assay systems using synthetic repair substrates that are actively transcribed even in the absence of Spt4 and Spt5. Taken together, Spt4 and Spt5 can function independently in multiple transcription-coupled steps of CSR

What is the significance of a positive Propionibacterium acnes culture around a joint replacement?

The purpose of this study was to show the significance of a positive Propionibacterium acnes sample around a joint replacement. Records from the microbiology laboratory data over a 3-year period were reviewed to identify patients with prosthetic joints from whom Propionibacterium acnes was isolated at least once. The medical records of all those patients were retrieved and the demographic, clinical, microbiological and haematological data were collected and examined. The preoperative values of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were recorded. Fifty patients underwent a routine revision of a joint arthroplasty; six patients had a joint aspiration. Only one patient had further revision surgery for infection. The preoperative values of ESR and CRP were very variable. The presence of a positive sample around a joint arthroplasty is of uncertain significance. Further studies are needed in order to establish uniform criteria for the diagnosis of infection caused by Propionibacterium acnes