Inhibition of Tat activity by the HEXIM1 protein

BACKGROUND: The positive transcription elongation factor b (P-TEFb) composed by CDK9/CyclinT1 subunits is a dedicated co-factor of HIV transcriptional transactivator Tat protein. Transcription driven by the long terminal repeat (LTR) of HIV involves formation of a quaternary complex between P-TEFb, Tat and the TAR element. This recruitment is necessary to enhance the processivity of RNA Pol II from the HIV-1 5' LTR promoter. The activity of P-TEFb is regulated in vivo and in vitro by the HEXIM1/7SK snRNA ribonucleic-protein complex. RESULTS: Here we report that Tat transactivation is effectively inhibited by co-expression of HEXIM1 or its paralog HEXIM2. HEXIM1 expression specifically represses transcription mediated by the direct activation of P-TEFb through artificial recruitment of GAL4-CycT1. Using appropriate HEXIM1 mutants we determined that effective Tat-inhibition entails the 7SK snRNA basic recognition motif as well as the C-terminus region required for interaction with cyclin T1. Enhanced expression of HEXIM1 protein modestly affects P-TEFb activity, suggesting that HEXIM1-mediated repression of Tat activity is not due to a global inhibition of cellular transcription. CONCLUSION: These results point to a pivotal role of P-TEFb for Tat's optimal transcription activity and suggest that cellular proteins that regulate P-TEFb activity might exert profound effects on Tat function in vivo

p14ARF Directly Interacts with Myc Through the Myc BoxII Domain.

Myc is a well known proto-oncogene encoding for a transcription factor whose activity is tightly regulated in the cellular context. Myc was the first oncogene recognized to activate the ARF tumor suppressor gene which suppresses cell proliferation partly through stabilization of the p53 tumor suppressor protein but which also has p53-independent growth-suppressive functions. Recent studies have indicated that mouse p19ARF negatively regulates Myc's transcriptional activity. We here show that the human p14ARF directly associates with Myc and relocates Myc from the nucleoplasm to the nucleolus. We found that p14ARF interacts with the Myc-Max complex and the binding of p14ARF does not interfere with Myc-Max interaction in vitro. Protein interaction assays define the Myc BoxII as a critical domain required for interaction with p14ARF. Moreover, we identify 30 amino acids encompassing Myc BoxII domain required for p14ARF interaction and colocalization in vivo. Finally, we show that p14ARF down regulates Myc activated transcription and that this activity cannot be addressed to an intrinsic p14ARF repressor domain

Statistical optimization of biohydrogen and ethanol production from crude glycerol by microbial mixed culture

7noneC. Varrone; B. Giussani; G. Izzo; G. Massini; A. Marone; A. Signorini; A. WangC., Varrone; Giussani, Barbara; G., Izzo; G., Massini; A., Marone; A., Signorini; A., Wan

Mesophilic biohydrogen production from buffalo slurry co-fermented with cheese whey and crude glycerol: Optimization using Mixture Design

Biohydrogen production from buffalo slurry (BS) co-fermented with cheese whey (CW) and crude glycerol (CG) was investigated using a suitable microbial community (F210) as inoculum. Mixture Design was used to individuate the optimal composition (%) of the three substrate components and to investigate the effect of the mixing ratio on Bio-H2 yields. Maximum H2 yield estimated through the model was around 117 mL H2/g VSadded, while the maximum experimentally detected was 111.6\ub121.8 mL H2/g VSadded, obtained for a mixing ratio of substrate composition of 66% BS and 33% CW (R2=0.962; p-value=0.0001). CW was clearly the most suitable substrate (with a relative contribution higher than 46%), but led to a rapid drop in pH from 6.5 to 4, while BS showed high buffering capacity by maintaining the pH above 6. The results demonstrate the usefulness of the mixture design for finding the optimal substrate composition using BS as co-fermentation substrate to obtain high H2 production yields. Moreover the response surface shows the possibility of mixing the substrates in different ways, while maintaining H2 production within an optimum range: 105-117 mL H2/g VSadded. This might offer a considerable advantage in the effective management of systems or processes in which the substrates availability may change over the time

Optimization of substrate composition for biohydrogen production from buffalo slurry co-fermented with cheese whey and crude glycerol, using microbial mixed culture

Biohydrogen production from buffalo slurry (BS) co-fermented with cheese whey (CW) and crude glycerol (CG) was investigated using a suitable microbial community (F210) as inoculum. Mixture Design was used to find the optimal composition (%) of the three substrate components and to investigate the effect of the mixing ratio on Bio-H2 yields. Maximum H2 yield estimated through the model was around 117 mL H2/g VSadded, while the maximum experimentally detected was 111.6 \ub1 21.8 mL H2/g VSadded, obtained for a mixing ratio of substrate composition of 66% BS and 33% CW (R2 = 0.962; p-value = 0.0001). CW was clearly the most suitable substrate (with a relative contribution higher than 46%), but led to a rapid drop in pH from 6.5 to 4, while BS showed high buffering capacity by maintaining the pH above 6. Interestingly, the co-digestion of the different substrates decreased the H2 production lag phase \u3bb; in particular the presence of BS shortened the lag period (\u3bb < 3 h) and increased the degradation efficiency of CG. The results demonstrate the usefulness of the mixture design for finding the optimal substrate composition, using BS as co-fermentation substrate to obtain high H2 production yields. Moreover the response surface shows the possibility of mixing the substrates in different ways, while maintaining H2 production within an optimum range: 105-117 mL H2/g VSadded. This might offer a considerable advantage in the effective management of systems or processes, in which the substrates availability may change over the time

La Balma dei Cervi a Crodo. Campagna di documentazione, di ricerca e attivit\ue0 di valorizzazione in un riparo con pitture rupestri preistoriche

L'articolo propone un approfondimento sulle ricerche in corso presso la Balma dei Cervi di Crodo in Valle Ossol