Abstract
I present a hypothesis that begins with the proposal that abiotic ancestors of phage RNA and DNA packaging systems (and cells) include mobile shells with an internal, molecule-transporting cavity. The foundations of this hypothesis include the conjecture that current nucleic acid packaging systems have imprints from abiotic ancestors. The abiotic shells (1) initially imbibe and later also bind and transport organic molecules, thereby providing a means for producing molecular interactions that are links in the chain of events that produces ancestors to the first molecules that are both information carrying and enzymatically active, and (2) are subsequently scaffolds on which proteins assemble to form ancestors common to both shells of viral capsids and cell membranes. Emergence of cells occurs via aggregation and merger of shells and internal contents. The hypothesis continues by using proposed imprints of abiotic and biotic ancestors to deduce an ancestral thermal ratchet-based DNA packaging motor that subsequently evolves to integrate a DNA packaging ATPase that provides a power stroke.
Highlights
Analysis of biotic motors has focused on the question of whether or not a power stroke occurs
Biasing of a thermal ratchet can occur via non-specific forces, such as those generated by either electrical fields or pressure gradients
(1) the components of today’s DNA packaging motors have ancient origin, (2) capsid expansion associated with nucleic acid packaging is an unexplained phenomenon that is potentially rooted in the ancient past, and (3) a thermal ratchet-based motor is likely to have been one of the earliest ancestors
Summary
Analysis of biotic motors (i.e., motors constructed with information from polymer coding) has focused on the question of whether or not a power stroke occurs. Biasing of a thermal ratchet can occur via non-specific forces, such as those generated by either electrical fields or pressure gradients These alternatives have been considered for actin/myosin, kinesin/tubulin, dynein/tubulin, ribosome/peptide and phage DNA packaging motors [1,2,3,4,5,6,7,8]. My explanation of data of all types produced the following proposal for the type one cycle: The DNA packaging ATPase ring acts as an ATP cleavage-driven, bind/release thermal ratchet that transfers energy to the connector; the connector delivers the power stroke [18]. One reasonably conjectures that each component of a power stroke-dependent biotic motor has an ancestor that was part of a thermal ratchet. The focus on nucleic acid packaging motors has the advantages of (1) the information already obtained for the present-day motors already studied (to be called classical motors) and (2) the potential information to be obtained, in the future, by detecting and characterizing additional present-day motors that are less evolved than the classical motors (pre-classical motors)
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