The degradation of some proto-oncogene and lymphokine mRNAs is controlled in part by an AU-rich element (ARE) in the 3' untranslated region. It was shown previously (G. Brewer, Mol. Cell. Biol. 11:2460-2466) that two polypeptides (37 and 40 kDa) copurified with fractions of a 130,000 x g postribosomal supernatant (S130) from K562 cells that selectively accelerated degradation of c-myc mRNA in a cell-free decay system. These polypeptides bound specifically to the c-myc and granulocyte-macrophage colony-stimulating factor 3' UTRs, suggesting they are in part responsible for selective mRNA degradation. In the present work, we have purified the RNA-binding component of this mRNA degradation activity, which we refer to as AUFl. Using antisera specific for these polypeptides, we demonstrate that the 37-and 40-kDa polypeptides are immunologically cross-reactive and that both polypeptides are phosphorylated and can be found in a complex(s) with other polypeptides. Immunologically related polypeptides are found in both the nucleus and the cytoplasm. The antibodies were also used to clone a cDNA for the 37-kDa polypeptide. This cDNA contains an open reading frame predicted to produce a protein with several features, including two RNA recognition motifs and domains that potentially mediate protein-protein interactions. These results provide further support for a role of this protein in mediating ARE-directed mRNA degradation.The c-myc gene is important for the control of cellular growth, differentiation, and transformation (reviewed in references 17 and 41). It belongs to the class of immediateearly genes whose expression is required to drive cells from Go to G1 following stimulation of quiescent cells by growth factors. However, the c-myc gene is not unique in terms of having an essential role in cellular growth processes. It has been known for decades that specific and timely changes in the expression of multiple genes are required for proper embryonic development and cell maturation (20). Expression of genes such as c-myc seems to be regulated not only at the levels of transcription, attenuation, nuclear processing, and translation but also at the level of mRNA turnover (reviewed in reference 41). Indeed, direct half-life measurements indicated that c-myc mRNA has a half-life of 15 to 40 min (19). These and other studies (41) demonstrated that the control of c-myc mRNA turnover might be an important means of regulating both the level and the timing of c-myc expression.Many proto-oncogene mRNAs are very unstable. The rapid turnover of c-myc mRNA is controlled by sequences in the 3' untranslated region (3'UTR) or by coding region sequences (reviewed in references 33 and 60). A common feature of many labile mRNAs, such as those for c-myc, c-fos, and granulocyte-macrophage colony-stimulating factor (GM-CSF), is the presence of an AU-rich element (ARE) in the 3'UTR which is one cis-acting element responsible for their rapid degradation (reviewed in reference 3, 48, and 60). It AUUUA (70). This might be important because...

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Urinary tract infections are the most common urologic disease in the United States and annually account for over 7 million office and 1 million emergency department visits. In adults, diagnosis of urinary tract infection is typically based on characteristic clinical features and abnormal laboratory values. Imaging is usually reserved for patients who do not respond to therapy and for those whose clinical presentation is either atypical or potentially life threatening. Urinary tract infection typically originates in the urinary bladder; when it migrates to the kidney or is seeded there hematogenously, a tubulointerstitial inflammatory reaction ensues, involving the renal pelvis and parenchyma. The condition is characterized as pyelonephritis. Complicated and uncomplicated pyelonephritis, xanthogranulomatous pyelonephritis, and tuberculosis are all urinary tract infections for which imaging evaluation adds diagnostic information important for patient care. Computed tomography (CT), when performed before, immediately after, and at delayed intervals from contrast material injection, is the preferred modality for evaluating acute bacterial pyelonephritis. CT is also preferred over conventional radiography and ultrasonography (US) for assessing emphysematous pyelonephritis. Xanthogranulomatous pyelonephritis is a chronic granulomatous process, induced by recurrent bacterial urinary tract infection. Although US is useful in the diagnosis of this condition, CT is the main imaging tool, as it provides highly specific findings and accurate assessment of the extrarenal extent of disease, which is essential for surgical planning. The increasing prevalence of tuberculosis and continued emergence of antibiotic-resistant strains have significance for genitourinary radiologists, as the urinary tract is the most common extrapulmonary site of tuberculosis. Familiarity with the renal manifestations of the disease--pelvoinfundibular strictures, papillary necrosis, cortical low-attenuation masses, scarring, and calcification--will help in the diagnosis, even in the absence of documented pulmonary disease.

Myelolipomas are adrenal or extra-adrenal masses, with hemorrhage more common in larger lesions (diameter, > 10 cm). The CT appearance of myelolipomatous foci, which can be found within other pathologic adrenal conditions, is different from that of isolated adrenal myelolipomas.

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