Part:BBa_K1172904

Rnase Ba (Barnase) from Bacillus amyloliquefaciens

Usage and Biology

The Barnase (EC 3.1.27) is a 12 kDa extracellular microbial ribonuclease, which is naturally found in the Gram-positive soil bacteria Bacillus amyloliquefaciens and consists of a single chain of 110 amino acids. The Barnase (RNase Ba) catalyses the cleavage of single stranded RNA, preferentially behind Gs. In the first step of the RNA-degradation a cyclic intermediate is formed by transesterification and afterwards this intermediate is hydrolyzed yielding in a 3'-nucleotide ([http://2013.igem.org/Team:Bielefeld-Germany/Biosafety/Biosafety_System_S#References Mossakowska et al., 1989]).

Figure 1: Enzymatic reaction of the RNA-cleavage by the RNase Ba. First the transesterification by the Glu-73 residue is performed and then this cyclic intermediate is hydrolyzed by the His-102 of the Barnase

In Bacillus amyloliquefaciens, the activity of the Barnase (RNase Ba) is inhibited intracellular by an inhibitor called barstar. Barstar consists of only 89 amino acids and binds with a high affinity to the toxic Barnase. This prevents the cleavage of the intracellular RNA in the host organism ([http://2013.igem.org/Team:Bielefeld-Germany/Biosafety/Biosafety_System_S#References Paddon et al., 1989]). Therefore the Barnase normally acts only outside the cell and is translocated under natural conditions. For the Biosafety-System araCtive we modified the enzyme by cloning only the sequence responsible for the cleavage of the RNA, leaving out the N-terminal signal peptide part.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

As shown in Figure 2 below, the transcription of the DNA, which encodes the Barnase produces a 474 nt RNA. The translation of the RNA starts about 25 nucleotides downstream from the transcription start and can be divided into two parts. The first part (colored in orange) is translated into a signal peptide at the amino-terminus of the Barnase coding RNA. This part is responsible for the extracellular translocation of the RNase Ba, while the peptide sequence for the active Barnase starts 142 nucleotides downstream from the transcription start (colored in red).
For the Biosafety-System araCtive, we only used the part (BBa_K1172904) of the Barnase encoding the catalytic domain without the extracellular translocation signal of the toxic gene product. Translation of the barnase gene leads to rapid cell death if the expression of the Barnase is not repressed by the repressor AraC of our Biosafety-System.

Figure 2: Sequence of the signal peptide amino terminal of the RNase Ba (Barnase). The Biobrick BBa_K1172904 does not contain the signal sequence for the extracellular translocation, but only the coding sequence for the mature enzyme.

References

• Mossakowska, Danuta E. Nyberg, Kerstin and Fersht, Alan R. (1989) Kinetic Characterization of the Recombinant Ribonuclease from Bacillus amyloliquefaciens (Barnase) and Investigation of Key Residues in Catalysis by Site-Directed Mutagenesis [http://pubs.acs.org/doi/pdf/10.1021/bi00435a033|Biochemistry 28: 3843 - 3850.].
• Paddon, C. J. Vasantha, N. and Hartley, R. W. (1989) Translation and Processing of Bacillus amyloliquefaciens Extracellular Rnase [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC209718/pdf/jbacter00168-0575.pdf|Journal of Bacteriology 171: 1185 - 1187.].
• Voss, Carsten Lindau, Dennis and Flaschel, Erwin (2006) Production of Recombinant RNase Ba and Its Application in Downstream Processing of Plasmid DNA for Pharmaceutical Use [http://onlinelibrary.wiley.com/doi/10.1021/bp050417e/pdf|Biotechnology Progress 22: 737 - 744.].