The centromeric regions in the fission yeast Schizosaccharomyces pombe are wrapped by nucleosomes containing the CENP-A histone H3 variant, and are flanked by clusters of tRNA genes that separate them from the surrounding pericentric heterochromatin. If the tRNA clusters are removed from this region, the HP1-bound heterochromatin spreads further to cover the centromeric regions. The tRNA genes are transcribed by strong RNA polymerase III promoters, which can associate with transcription factors and recruit chromatin-modifying enzymes.
Based on these observations, indicate which blanks (A to E) in the paragraph below correspond to each of the following phrases. Your answer would be a five-letter string composed of letters A to E only, e.g. BCDEA.
"The …(A) are not sufficient to prevent heterochromatin expansion to the centromeric regions. Instead, the …(B) are acting as …(C) in S. pombe, similar to the role of the …(D) in the ?-globin locus in chickens and humans. Likely candidates for the histone-modifying enzymes recruited by the RNA polymerase III complexes are …(E)."
( ) HS4 element
( ) chromatin boundaries
( ) histone acetyl transferases
( ) tRNA genes
( ) CENP-A-containing histones