Functional eukaryotic nuclear localization signals are widespread in terminal proteins of bacteriophages

Abstract

A number of prokaryotic proteins have been shown to contain nuclear localization signals (NLSs), although its biological role remains sometimes unclear. Terminal proteins (TPs) of bacteriophages prime DNA replication and become covalently linked to the genome ends. We predicted NLSs within the TPs of bacteriophages from diverse families and hosts and, indeed, the TPs of Φ29, Nf, PRD1, Bam35, and Cp-1, out of seven TPs tested, were found to localize to the nucleus when expressed in mammalian cells. Detailed analysis of Φ29 TP led us to identify a bona fide NLS within residues 1-37. Importantly, gene delivery into the eukaryotic nucleus is enhanced by the presence of Φ29 TP attached to the 5′ DNA ends. These findings show a common feature of TPs from diverse bacteriophages targeting the eukaryotic nucleus and suggest a possible common function by facilitating the horizontal transfer of genes between prokaryotes and eukaryotes.

My Life with Bacteriophage φ29

“…Analysis of 29 TP led us to identify a bona fide nuclear localization signal within residues 1-37. Importantly, gene delivery into the eukaryotic nucleus was enhanced by the presence of 29 TP attached to the 5Ј-DNA ends (36). These findings show a common feature of TPs from diverse bacteriophages targeting the eukaryotic nucleus and suggest a possible common function by facilitating the horizontal transfer of genes between prokaryotes and eukaryotes.…”

Multiple roles of genome-attached bacteriophage terminal proteins

“…Other prokaryotic proteins that are tightly bound to DNA molecules, like Agrobacterium VirD2, also have intrinsic NLSs required for DNA transfer to the eukaryotic nucleus (Rossi et al, 1993;Pelczar et al, 2004). Interestingly, we found that Φ29 TP also localizes in the eukaryotic nucleus when expressed in mammalian cells and, moreover, the presence of Φ29 TP at both ends of a linear DNA enhances gene delivery (Redrejo- Rodríguez et al, 2012). This nuclear targeting relies on the N-terminal residues 1-37 and, like cellular NLSs, its function requires energy, thereby suggesting that the phage TP contains an intrinsic bona fide NLS.…”

“…Moreover, structure-function studies from other phage TPs beyond Φ29 or Φ29-like phages are not available, therefore their structural or functional domains are not easy to recognize. However, as expected from proteins that perform the same function, they share some structural features (Table 1), like a relatively small size and a high proportion of basic residues, some of them grouped in positively charged clusters in the N-terminal half of the protein (Redrejo- Rodríguez et al, 2012), which usually results in a high isoelectric point. Moreover, although the priming residue may be a serine, threonine or tyrosine, it is always in a loop between two α-helices and followed by an acidic residue (D/E), which has been recently shown to be involved in the stabilization of the priming loop/DNAP catalytic active site interaction (del Prado et al, 2013).…”

“…The structure of Φ29 TP has been partially solved (Kamtekar et al, 2006); it contains three structural domains: (i) the Cterminal domain (Ct), which has the serine-232 priming residue, (ii) the intermediate domain (I) that contributes to the surface of interaction with the DNAP, and (iii) the N-terminal domain (Nt) that has sequence-independent DNA-binding capacity required for recruitment of the viral genome (TP-DNA) and DNAP at the host nucleoid (Muñoz-Espín et al, 2010) and also contains a nuclear localization sequence (NLS), functional when the protein is expressed in mammalian cells (Redrejo-Rodríguez et al, 2012). In the case of Adenovirus, the TP is synthesized as pre-terminal protein (pTP), which is processed by a viral-encoded protease to yield mature TP after the viral replication cycle starts.…”

My scientific life

“…It is important to stress the fact that gene delivery into the eukaryotic nucleus was enhanced by the presence of ø29 TP attached at the 5' ends. 16 I would also like to mention some phage-host interactions in ø29 development. The early gen e56 encodes p56, a protein of 56 amino acids.…”