Pneumomediastinum and pneumoretroperitoneum

A 23-year-old man presented to the emergency department with extensive subcutaneous emphysema and severe dehydration after a prolonged self-imposed religious fast. Chest radiographs showed marked pneumomediastinum and pneumoretroperitoneum without pneumothorax. Patients are often admitted to the hospital for close observation when these findings are recognized, but this caution is generally unwarranted. This case illustrates the common occurrence of the usually benign entity of pneumomediastinum without pneumothorax.

Evolution of keratin genes: different protein domains evolve by different pathways

Intermediate filaments are composed of a family of proteins that evolved from a common ancestor. The proteins consist of three domains: a central, alpha-helical domain similar in all intermediate filaments, bracketed by two domains that are variable in length and structure. Within the intermediate-filament family, several subfamilies have been recognized by immunologic and nucleic acid hybridization techniques. In this paper we present the sequence of the genomic DNA coding for a 65-kilodalton human keratin and compare it with the sequences of other intermediate-filament proteins. While the central, alpha-helical domains of these proteins show homologies that indicate a common ancestor, the sequences of the variable terminal domains indicate that the variable domains evolved through a series of tandem duplications and possibly by gene-conversion mechanisms.

Ribonucleotides are channeled into a mixed DNA-RNA polymer by permeabilized hamster cells

Permeabilized CHEF/18 hamster cells incorporate label from [3H] cytidine diphosphate (CDP) into material that we had designated as DNA. Spyrou and Reichard reported this label was incorporated only into RNA. To resolve this discrepancy the studies reported here were performed. We demonstrate incorporation into a DNA polymer with major interspersed RNA sequences. Incorporation into deoxycytidine isolated from this product was little diluted by a great excess of unlabeled dCTP, confirming channeling under these conditions of CDP into polymerized deoxyribonucleotides.