Translocation and proteolytic processing of nascent secretory polypeptide chains: two functions associated with the ribosomal domain of the endoplasmic reticulum

Rat liver microsomes were subfractionated by isopycnic centrifugation in sucrose gradient. The subfractions were assayed for translocation and proteolytic processing of nascent polypeptides in a rabbit reticulocyte lysate programmed with total RNA from human term placenta. The distribution of the translocation and processing of prelactogen through the gradient correlated with that of the microsomal RNA (ribosomes). Microsomes became inactive upon incubation with elastase, but the proteolyzed membranes recovered their activity by recombination with the soluble and active fragment of the docking protein (SRP-receptor) from dog pancreas. When this fragment was combined with the gradient subfractions, or with the subfractions inactivated by incubation with elastase, the density profile of the translocation activity remained similar to that of RNA. Thus, its distribution cannot be accounted for merely by that of the docking protein; another membrane constituent, still unidentified, is both necessary for translocation of polypeptides and restricted to the rough portions of the endosplamic reticulum. Signal peptidase was assayed in the absence of protein synthesis, by use of preformed prelactogen and detergent-disrupted microsomes. Its density distribution was also similar to that of RNA. Several components of the endosplamic reticulum now appear to be segregated within restricted areas on either side of the membrane, and to make up a biochemically distinct domain. We propose to call it the ribosomal domain in consideration of its contribution to protein biosynthesis by bound ribosomes. This domain probably accounts for a greater part of the membrane area at the cytoplasmic than at the luminal surface, as postulated earlier to explain how enzymes of the cytoplasmic surface are relatively less abundant in the rough microsomes than those of the luminal surface [Amar-Costesec A. & Beaufay H. (1981) J. Theor. Biol. 89, 217-230].     

Anatomical brain asymmetry in monkeys: frontal, temporoparietal, and limbic cortex in Macaca

Measurements evaluating possible cerebral hemispheric asymmetries were taken by hand on frontal, parietal, and temporal cortex on 60 formalin-fixed Macaca mulatta and Macaca fascicularis brain specimens. No statistically significant (P less than 0.05) right/left side differences in the mean length of four sulci in visual-processing areas of the cortex were found. The sulcus adjacent to the region cytoarchitecturally homologous to the motor speech area in the human brain did not show pronounced asymmetry. In both species, however, a small parietal lobe sulcus showed greater development on the left hemisphere than in the right. In measurements made using digital planimetry, right/left side differences in the area of the dorsal cingulate gyrus were not found. Behavioral evidence suggests that monkeys do not exhibit a consistent pattern of cerebral dominance for functions associated with most of these regions of the brain.     

脑片诱发电位计算机处理系统及其使用实例

用计算机处理脑片诱发电位可大大提高数据处理效率和信息提取率,并使大量、连续观察成为可能,本系统数据采集板与计算机之间采用DMA方式进行数据传送,包括采样子程序在内的全部处理程序均用高级BASIC语言编写,文中介绍了该程序各项功能和有关编程技巧以及海马脑片实验中的应用实例。     

C1q,a collagen-like complement subcomponent,in dermatosparactic cattle: its extracellular modification is not affected by lack of procollagen N-terminal proteinase (pN-proteinase)

C1q, a collagen-like complement protein, was purified from the serum of a ddermatosparactic calf which lacks procollagen N-terminal proteinase (pN-proteinase). The specific hemolytic activity of the serum Clq from the dermatosparactic animal was identical to that of C1q from a normal calf. Gel-filtration of serum from dermatosparactic calf, on Sepharose 6B, showed the presence of C1q-antigenic material at only one position which was identical to the elution position of normal bovine C1q. No differdence, under dissociating conditions, could be seen in the size of the chains of C1q in specific immunoprecipitates isolated from the sera of dermatosparactic and normal animals, as judged by polyacrylamidegel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS). The C1q from the dermatosparactic animal showed the same N-terminal amino acid and typtic-digest peptide pattern on HPLC as C1q from the normal calf. These results strongly suggest that pN-proteinase is not involved in the extracellular processing of C1q.     

Histamine-like immunoreactivity in photoreceptors of the compound eyes and ocelli of the flies Calliphora erythrocephala and Musca domestica

Summary Antibodies to histamine were used for immunocytochemical studies of the visual system in the flies Calliphora erythrocephala and Musca domestica. Specific immunolabeling of photoreceptors was found both in the compound eyes and ocelli of both species. In the compound eyes histamine-like immunoreactivity (HA-IR) was found in all the short visual fibers (photoreceptors R1–6) and one type of long visual fiber (photoreceptor R8). In addition, the ocellar photoreceptors also show HA-IR. In view of earlier biochemical and pharmacological/physiological findings by Elias and Evans (1983) and Hardie (1987) it thus seems likely that histamine is a neurotransmitter in insect photoreceptors. Interestingly, the second type of long visual fiber (photoreceptor R7) has recently been found to be GABA-immunoreactive (Datum et al. 1986). The two types of long visual fibers may hence use different transmitters which act on different receptors of the postsynaptic neurons in the second visual neuropil, the medulla. In addition to the photoreceptors in the retina and ocelli, we found processes of HA-IR neurons in one of the optic lobe neuropils, the lobula. This finding indicates that histamine may also be a transmitter in certain interneurons in the visual system.Abbreviations HA histamine - GABA -amino butyric acid - GAD glutamic acid decarboxylase - 5-HT 5-hydroxytryptamine (serotonin) - HA-IR histamine-like immunoreactivity - R1-R6 class of short-axoned photoreceptors - R7 and R8 long-axoned photoreceptors - LMC large monopolar neuron of lamina - HSA human serum albumin - PBS phosphate-buffered saline - DEPC diethylpyrocarbonate     

Assembly of the barley light-harvesting chlorophyll a/b proteins in barley etiochloroplasts involves processing of the precursor on thylakoids

A barley gene encoding the major light-harvesting chlorophyll a/b-binding protein (LHCP) has been sequenced and then expressed in vitro to produce a labelled LHCP precursor (pLHCP). When barley etiochloroplasts are incubated with this pLHCP, both labelled pLHCP and LHCP are found as integral thylakoid membrane proteins, incorporated into the major pigment-protein complex of the thylakoids. The presence of pLHCP in thylakoids and its proportion with respect to labelled LHCP depends on the developmental stage of the plastids used to study the import of pLHCP. The reduced amounts of chlorophyll in a chlorophyll b-less mutant of barley does not affect the proportion of pLHCP to LHCP found in the thylakoids when import of pLHCP into plastids isolated from the mutant plants is examined. Therefore, insufficient chlorophyll during early stages of plastid development does not seem to be responsible for their relative inefficiency in assembling pLHCP. A chase of labelled pLHCP that has been incorporated into the thylakoids of intact plastids, by further incubation of the plastids with unlabelled pLHCP, reveals that the pLHCP incorporated into the thylakoids can be processed to its mature size. Our observations strongly support the hypothesis that after import into plastids, pLHCP is inserted into thylakoids and then processed to its mature size under in vivo conditions.     

The effect of pulse repetition rate on the delay sensitivity of neurons in the auditory cortex of the FM bat,Myotis lucifugus

1. Echo delay is the primary cue used by echolocating bats to determine target range. During target-directed flight, the repetition rate of pulse emission increases systematically as range decreases. Thus, we examined the delay tuning of 120 neurons in the auditory cortex of the bat, Myotis lucifugus, as repetition rate was varied. 2. Delay sensitivity was exhibited in 77% of the neurons over different ranges of pulse repetition rates (PRRs). Delay tuning typically narrowed and eventually disappeared at higher PRRs. 3. Two major types of delay-sensitive neurons were found: i) delay-tuned neurons (59%) had a single fixed best delay, while ii) tracking neurons (22%) changed their best delay with PRR. 4. PRRs from 1-100/s were represented by the population of delay-sensitive neurons, with the majority of neurons delay-sensitive at PRRs of at least 10-20/s. Thus, delay-dependent neurons in Myotis are most active during the search phase of echolocation. 5. Delay-sensitive neurons that also responded to single sounds were common. At PRRs where delay sensitivity was found, the responses to single sounds were reduced and the responses to pulse-echo pairs at particular delays were greater than the single-sound responses. In facilitated neurons (53%), the maximal delay-dependent response was always larger than the best single-sound responses, whereas in enhanced neurons (47%), these responses were comparable. The presence of neurons that respond maximally to single sounds at one PRR and to pulse-echo pairs with particular echo delays at other PRRs suggests that these neurons perform echo-ranging in conjunction with other biosonar functions during target pursuit.     

Expectancy controlled sampling decisions in Vimba elongata

Synopsis Experimental data on snapping behavior of laboratory reared zährte, Vimba elongata, indicate that this species chooses between different food searching methods. If visibility is good, mainly directed snaps are employed for immediate food location. However, under conditions of reduced visibility undirected snapping and sampling methods are adopted. In the field, zährte may use sampling to acquire foraging benefits from stochastically distributed, hidden resources, like sediment dwelling prey. In the experiments this species continued to sample the bottom even in situations without any chance of prey detection. It is therefore concluded that zährte's searching decisions, apart from incorporating external information on prey occurrence, are controlled by internal expectations of long term benefits derived from sampling.