description=This graceful moon caught orbiting a planet is actually something much more ominous. A scanning electron microscope (SEM) has captured the protein core of a retrovirus moving toward a pore hole in the nucleus of a host cell (lower left). The protein core enables the conversion of nucleic acid from the virus (in the form of RNA) into DNA to match the host cell genes. Thus, the virus replicates. Some retroviruses are known to contain at least 20 different genes that can cause cancer (oncogenes). ìÄ
