RNA polymerase II is a multisubunit protein that transcribes protein coding genes in eukaryotes. One of its most interesting structural features is that its largest subunit has 52 repeats (in humans) of a seven amino acids repeat with the sequence YSPTSPS. This part of the protein, which is more than 350 amino acids long, is unstructured (this means it stays elongated, without folding into regular secondary structures of compact globular regions) and it's repeated phosphorylated by protein kinases as it transcribes through a gene. Examine the sequence of this seven amino acid repeat, and clearly explain 1) why is this domain unstructured and 2) why is this sequence such a good substrate for protein kinases.