The "fos" proto-oncogene codes for a component of the AP1 transcription factor, an important regulator of gene expression and cell proliferation. Dysregulation of AP1 function may lead to the malignant transformation of the cell. The present test describes an experiment in which the role of a micro-RNA (miR-7b) in the regulation of "fos" gene expression was studied. miR-7b shows partial sequence complementarity to the 3'-untranslated region of "fos" mRNA. A DNA fragment coding for miR-7b RNA, and another fragment coding for a micro-RNA unrelated to "fos" mRNA were cloned into expression vectors, and the recombinant plasmids (designated si-miR-7b and si-miR-neg) were transfected into mouse fibroblasts; nontransfected cells were used as controls. Some of the cultures were treated with a phorbol ester (phorbol myristate acetate (PMA)), while others were left untreated. Two hours after PMA treatment protein extracts were prepared from the cultures and were then subjected to Western blot analysis using anti-Fos and antiactin antibodies. RNA was isolated from other cell cultures after 1 hour PMA treatment, subjected to formaldehyde/agarose gel electrophoresis and ethidium bromide staining followed by Northern blotting using a "fos" cDNA probe. Before analyzing the results of the experiment, one should recall their factual knowledge required to understand the theoretical background of this study. This article presents a five-choice completion question consisting of a question or incomplete statement followed by five suggested answers or completions. It then presents (1) a figure analysis, consisting of statements that are related to the information presented in the description of the experiment; and (2) a relationship analysis, consisting of a sentence with two main parts: an assertion and a reason for that assertion. Correct answers for each question and analysis are provided. (Contains 1 figure.)