The direct regulators of differential gene expression are typically

transcription factors.
enzymes.
signaling molecules.
cell surface receptors.

The correct answer is: transcription factors.

Gene expression is controlled (regulated) on different levels (DNA structure, transcription, RNA processing, post-translational modification. Gene expression is regulated in order to increase or decrease the production of specific gene products.

Transcription factors can enhance the interaction between RNA polymerase and a DNA sequence- promoter, encouraging the expression of the gene. Such transcription factors are called activators. Otherwise, when the gene expression is inhibited, factors are called repressors and they bind to sequence –operator.

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.