At the lowest level, compaction is achieved by wrapping stretches of DNA around a core of histone proteins to form nucleosomes in a “beads on a string” configuration: 147 base pairs of DNA per nucleosome, with linkers of variable length between nucleosomes. The nucleosome core particle (NCP), or one “bead”, consists of 4 types of histone (H2A, H2B, H3, and H4), each of which has a compact core plus a positively-charged, flexible tail that protrudes from the core.

Like many other bacteria, Rickettsia uses the actin cytoskeleton of the host cells to move within a cell and spread from one cell to another. It does this through the agency of a “comet tail” assembled from actin filaments, and inhibition of comet tail formation reduces the virulence of Rickettsia. The bacterial transporter protein Sca2 is required for assembly of comet tails; it functions similarly to the eukaryotic formin proteins in promoting actin filament formation.

Insight into this question has biomedical significance, as membrane proteases are required for the cleavage of transmembrane anchors to release signaling proteins from the membrane, and disruption of this process is implicated in more than a dozen diseases. For example, the intramembrane rhomboid proteases are implicated in Parkinson's disease and parasite invasion.

Electrostatic interactions are important for both phases, and conformational changes occurring in an enzyme during its catalytic cycle modify these interactions. For complete understanding of the catalytic process, we require knowledge of the contribution of electrostatic effects to each step in the process, as well as an understanding of how conformational changes affect the electrostatic environment in the active site.

This is especially important when illuminating very small samples, as in protein microcrystallography where crystals can be on the order of a micron across and diffract weakly compared to larger crystals. Any excess scatter in these conditions will contribute unwanted noise and decrease the overall signal-to-noise ratio – an important measure of data quality. Consider an experiment where you first must take the water from a firehose and somehow get a water thread thinner than a human hair without any mist! That is akin to the scale of creating x-ray microbeam at CHESS.

At a later stage, 3-nucleotide RNA sequences are translated into protein according to the genetic code.