Proteolipid protein (PLP), the major myelin protein in the central nervous system (CNS), is also made by Schwann cells (SC) in the peripheral nervous system (PNS) but is not incorporated into the SC myelin sheath. We analyzed several PLP cDNA clones isolated from a rat sciatic nerve cDNA library and found that their coding sequences were identical to PLP cDNAs previously isolated from the CNS. In addition, we have discovered an unusual form of PLP message, present in both brain and sciatic nerve RNA, that is likely formed by alternative splicing within the 3' untranslated region of the primary PLP transcript. The absence of PLP from the SC myelin sheath thus cannot be explained by an alteration in its amino acid sequence. Steady-state levels of PLP mRNA in SC cultures treated with the cAMP analogue dibutyryl cAMP (dBcAMP) were not increased, whereas dBcAMP increased steady-state levels of mRNA encoding the major myelin protein, P0. We have also shown that expression of PLP, unlike that of P0, is regulated in SC in vitro at a posttranscriptional level. Finally, the steady-state levels of P0 mRNA are much more dramatically reduced than those of PLP mRNA during Wallerian degeneration of the peripheral nerve. Thus PLP expression in the PNS is probably controlled by different molecular mechanisms from P0, and may not be part of the coordinate program of myelin gene expression. In contrast to its expression in the PNS, transcription of PLP in the CNS is coordinately regulated along with the other myelin protein genes, suggesting there may be differences in the cis-acting elements and transacting factors involved in the regulation of PLP transcription in SC and oligodendrocytes (OC). Consistent with this notion, we have found that most PLP transcripts are initiated at the more proximal of two start sites in the PNS, while in the CNS proportionally more PLP transcripts are initiated from the distal start site. We propose that the proximal site, utilized predominantly in SC, is responsible for maintenance expression of PLP and is not inducible, while the distal site is responsible for the rapid, inducible increase of PLP message during brain development.

We examined the expression of mRNA encoding proteolipid protein (PLP), the major myelin protein in the CNS, in developing rat cerebrum, and in normal and degenerating optic nerves. PLP transcripts were initiated at two clusters of start sites that were separated by about 30 base pairs. During the peak of PLP mRNA expression in developing cerebrum, a higher proportion of PLP transcripts were initiated from the distal start site, furthest from the open reading frame, than in mature cerebrum. We enucleated one eye of immature rats to cause Wallerian degeneration in the optic nerve. In these degenerating optic nerves, the steady state levels of PLP mRNA fell markedly, and the proportion of distally initiated PLP transcripts declined to the same proportion found in normal adult nerves. Changes in myelin gene expression were not limited to PLP mRNA, as the steady-state levels of myelin basic protein (MBP) mRNA paralleled those of PLP mRNA in the developing cerebrum and in degenerating optic nerves. Thus, oligodendrocytes require axons to maintain their normal levels of PLP and MBP transcripts and the high proportion of distally initiated PLP transcripts that characterize early myelination.

Upon infection of Escherichia coli with bromodeoxyuridine-labeled T4 phage that had received 10 lethal hits of UV irradiation, a sizable amount of phage DNA was synthesized (approximately 36 phage equivalent units of DNA per infected bacterium), although very little multiplicity reactivation occurs. This progeny DNA was isolated and analyzed. This DNA was biased in its genetic representation, as shown by hybridization to cloned segments of the T4 genome immobilized on nitrocellulose ifiters. Preferentially amplified areas corresponded to regions

The de novo purine biosynthetic enzymes 5-amino-4-imidazolecarboxamide-ribonucleotide (AICAR) transformylase (EC 2.1.2.3), IMP cyclohydrolase (EC 3.5.4.10) and glycineamide-ribonucleotide (GAR) synthetase (EC 2.1.2.2) are encoded by the purHD locus of Escherichia coli. The DNA sequence of this locus revealed two open reading frames encoding polypeptides of Mr 57,335 and 45,945 (GAR synthetase), respectively, that formed an operon. The DNA sequence, maxicell and complementation analyses all supported the concept that the Mr 57,335 polypeptide is the product of the purH gene and encodes a bifunctional protein containing both AICAR transformylase and IMP cyclohydrolase activities. The 5' end of the purHD mRNA was determined by primer extension mapping and contains two regions of dyad symmetry capable of forming 'hairpin' loops where the formation of the one would prevent the formation of the other but not vice versa. Regulation by the purR gene product was explained by the discovery of a purR binding site in the purHD control region.

Abstract.A case of fatal nonneurological equine herpesvirus 1 (EHV-1) infection in a yearling filly is described. Gross lesions included extensive pulmonary edema, prominent laryngeal lymphoid follicles, and congestion and edema of the dorsal third ventricle choroid plexus. Histologically, there was vasculitis, hemorrhage, and edema in the lungs and dorsal third ventricle choroid plexus as well as mild intestinal crypt necrosis with occasional intranuclear inclusion bodies. The perivascular and vascular inflammatory infiltrates were comprised mainly of T lymphocytes and macrophages. EHV-1 antigen was identified within the nucleus and cytoplasm of endothelial cells, dendritic-like cells of the pharyngeal lymphoid follicles, pharyngeal glandular epithelium, crypt enterocytes, and monocytes. Attempted virus isolation was negative. Weak seroconversion for EHV-1 was observed. Herpesvirus-like particles were identified within pharyngeal endothelial cells by transmission electron microscopy. Polymerase chain reaction amplified 369 and 188 base-pair fragments specific for EHV-1. The scarcity of pathognomonic viral inclusions and lesions in this case suggests that this disease may not be recognized, particularly in situations when ancillary laboratory procedures are limited.Key words: Equine herpesvirus; horses; immunohistochemistry; polymerase chain reaction; vasculitis.Equine herpesvirus (EHV-1) causes abortion, stillbirth, respiratory disease, and encephalomyelopathy secondary to vasculitis in horses. 4,5,10,18 The infection is almost uniformly fatal in newborn foals. The outcome of the neurological form is variable, with some cases leading to paraplegia, quadriplegia, recumbency, and death or euthanasia due to the critical condition of the patient. We describe a fatal, nonneurological EHV-1 infection in a yearling filly associated with multisystemic vasculitis, severe pulmonary edema and hemorrhage, and mild enterotyphlocolitis, with particular emphasis on the distribution of the EHV-1 antigen (EHV-1Ag) identified with the avidin-biotin complex (ABC) indirect immunoperoxidase histochemical technique on affected tissues.A yearling Thoroughbred filly presented with a history of fever (up to 105 F), depression, and lethargy of a few days duration. Several other horses on the property were also febrile. These animals had not been vaccinated for equine respiratory viral pathogens. The filly was treated for pyrexia with nonsteroidal anti-inflammatory agents. She was found dead in her stall the morning of presentation.On necropsy, the mucous membranes were severely congested and cyanotic. There were approximately 5 liters of clear yellow-orange watery fluid in the thoracic cavity (Fig. 1). Similar fluid infiltrated and expanded the interlobular septa and visceral pleura of the lungs, which were very heavy. The trachea contained abundant froth, which extended to bronchi and bronchioli in association with fibrin. The lymphoid follicles around the epiglottis were prominent. The meningeal blood vessels were moderately hyperemi...