The Unusual Linear Plasmid Generating Systems of Prokaryotes

Abstract

Linear DNA is vulnerable to exonuclease degradation and suffers from genetic loss due to the end replication problem. Eukaryotes overcome these problems by locating repetitive telomere sequences at the end of each chromosome. In humans and other vertebrates this noncoding terminal sequence is repeated between hundreds and thousands of times, ensuring important genetic information is protected. In most prokaryotes, the end-replication problem is solved by utilizing circular DNA molecules as chromosomes. However, some phage and bacteria do store genetic information in linear constructs, and the ends of these structures form either invertrons or hairpin telomeres. Hairpin telomere formation is catalyzed by a protelomerase, a unique protein that modifies DNA by a two-step transesterification reaction, proceeding via a covalent protein bound intermediate. The specifics of this mechanism are largely unknown and conflicting data suggests variations occur between different systems. These proteins, and the DNA constructs they produce, have valuable applications in the biotechnology industry. They are also an essential component of some human pathogens, an increased understanding of how they operate is therefore of fundamental importance. Although this review will focus on phage encoded protelomerase, protelomerases found from Agrobacterium and Borellia will be discussed in terms of mechanism of action.

Bacteria have numerous distinctive groups of phage–plasmids with conserved phage and variable plasmid gene repertoires

“…P1 also encodes the site-specific Cre-recombinase to resolve head-to-tail multimers ( 7 ), which has become a versatile tool in genetic engineering ( 20 , 21 ). N15 has a linear dsDNA genome with covalently closed ends produced by a protelomerase (TelN) ( 22 ), and is a model system to study the formation, resolution and diversity of linear replicons in Bacteria ( 23 ). A few P–Ps closely related to P1 and N15 have been reported ( 9 , 24 ), but their numbers and diversity are poorly known.…”

Bacteria have numerous phage-plasmid families with conserved phage and variable plasmid gene repertoires

“…P1 also encodes the site-specific Cre-recombinase to resolve head-to-tail multimers (7), which has become a versatile tool in genetic engineering (20,21). N15 has a linear dsDNA genome with covalently closed ends produced by a protelomerase (TelN) (22), and is a model system to study the formation, resolution and diversity of linear replicons in Bacteria (23). A few P-Ps closely related to P1 and N15 have been reported (9,24), but their numbers and diversity are poorly known.…”