Gravity was a new set of challenges: simulated weightlessness, the physics of space, replicating complex machinery – all compounded by ambitiously long takes.
Translesion synthesis (TLS) is a DNA damage tolerance process that allows the DNA replication machinery to replicate past DNA lesions such as thymine dimers or AP sites.
In the latter case, viruses need to infect the cells, manipulate the host replication machinery to replicate their genomes and get released from the infected cells without killing the host or triggering the immune system.
DNA replication machinery cannot replicate the very ends of chromosomal DNA, known as the end replication problem, and this would result in the gradual loss of telomeres after each round of DNA replication, unless new telomeric DNA was synthesized by telomerase.
One major function of the early adenoviral gene products, such as E1A and E1B, is to push the infected cell into the S phase of the cell cycle (Flint and Shenk, 1997), since it is necessary for the virus in order to use the cellular DNA replication machinery to replicate its own genome efficiently.
Such genomic expansion was likely facilitated by the evolution of DNA replication machinery capable of replicating larger genomes [ 63].
The correlation of the degree of GC skew between bacterial plasmids and their host chromosomes suggests that these replicons within the same cells have replicated using the same replication machinery.
The addition of telomeric repeats relies on the activity of the telomerase enzyme [ 138], a specialized reverse transcriptase that compensates for the erosion that results from the inability of the semiconservative DNA replication machinery to fully replicate chromosome ends [ 139, 140].
Due to the inability of the semiconservative DNA replication machinery to fully replicate DNA ends of linear chromosomes, terminal chromosomal DNA is lost with each cell division, which, in the absence of a mechanism to restore telomere length, eventually leads to critically short telomeres and cellular senescence or apoptosis.
The DNA replication machinery is unable to replicate telomeres completely.
