Practice Questions

TLS Online TPP Program

#Question id: 2888

Repressive complexes have been discovered that are composed of multiple repressing proteins bound to RNAs many kilobases in length that do not contain long open reading frames and are consequently called long noncoding RNAs or lncRNAs. Which of the following statements is correct regarding the regulation of these lncRNAs?

#Unit 2. Cellular Organization

X inactivation is controlled by a roughly 100-kb domain on the X chromosome called the X-inactivation center that encodes a lncRNA known as XIST that is responsible for inactivation of the maternally derived chromosome.
Depletion of a 2.2-kb noncoding RNA expressed from the HOXC locus by siRNA unexpectedly led to derepression of the HOXD locus, a roughly 40-kb region on another chromosome encoding several Hox proteins and multiple other noncoding RNAs, in these cells.
HOTTIP lncRNA, which is transcribed from the 5’end of the HOXA locus, is proposed to coordinate the activation of HOXA genes by binding to a histone H3 lysine 9 methylase represents the cis activation by lnc-RNAs.
In humans, but not in mice, a lncRNA called XACT has been discovered to associate with multiple sites along the full length of the active X chromosome and is postulated to contribute to repression of gene activity on that chromosome.