A comparison was made of slocking rates of 4-7, 5-6 and 6-4 cows ha"' during the first 7 weeks (period I) of the grazing season. Each group of British Friesian cows was continuously stocked on a day and a night field. In the subsequent periods 2 and 3 (each lasting 7 weeks) the three groups were maintained at the same stocking rate within periods {4-2 and 31 cows ha', respectively). The differential stocking rates were achieved by the addition and removal of cows.The stocking rates applied in period 1 had no significant effects on milk yield, milk composition, liveweight change or condition score, in any period. Milk production ha"' over the three periods totalled 12390,13978 and 14986 kg, and the estimated utilized metaboiizable energy totalled 773, 81-5 and 86-6 GJ ha ' for low, medium and high stocking rates, respectively.Increased stocking rate in period I was associated with a decrease in sward height in periods 1 and 2. This led to an increase in herbage metaboiizable energy, and crude protein contents, and to an increase in tiller population density. The lowest stocking rate gave greater live individual tiller weights throughout the experiment and a longer interval between defoliation of individual tillers in period 1.The results indicate that high stocking rates in the spring are not necessarily detrimental to Correspondence: Dr J. D. Leaver, The West of Scotland .Agricultural College, Crichlon Royal Farm, Dumfries DGI 4SZ. UK. • Present address: Faculty of Agriculture, tJniversity of Newcastle, Newcasitc-upon-TyneNEI 7RU, UK.overall summer performance of spring calving dairy cows. However, high stocking rates in the early season ensure a high level of herbage utilization and milk output ha"' in that period. Although this practice leads to a reduced sward height in mid season, the sward has less rejected area, a higher tiller population density and a higher digestibility than swards stocked at a lower level.

Ribosomal protein S4 from Escherichia coli binds a large domain of 16 S ribosomal RNA and also a pseudoknot structure in the ␣ operon mRNA, where it represses its own synthesis. No similarity between the two RNA binding sites has been detected. To find out whether separate protein regions are responsible for rRNA and mRNA recognition, proteins with N-terminal or C-terminal deletions have been overexpressed and purified. Protein-mRNA interactions were detected by (i) a nitrocellulose filter binding assay, (ii) inhibition of primer extension by reverse transcriptase, and (iii) a gel shift assay. Circular dichroism spectra were taken to determine whether the proteins adopted stable secondary structures. From these studies it is concluded that amino acids 48 -104 make specific contacts with the mRNA, although residues 105-177 (out of 205) are required to observe the same toeprint pattern as fulllength protein and may stabilize a specific portion of the mRNA structure. These results parallel ribosomal RNA binding properties of similar fragments (Conrad, R. C., and Craven, G. R. (1987) Nucleic Acids Res. 15, 10331-10343, and references therein). It appears that the same protein domain is responsible for both mRNA and rRNA binding activities.Functional studies of ribosomes have tended to focus on the roles of the ribosomal RNAs in recent years, as a number of studies have uncovered specific contributions of different rRNA domains to ribosome activities (1). As more ribosomal protein sequences have become available, it is becoming clear that a number of these proteins are highly conserved among all organisms and must also have specific and necessary roles in ribosome function. An intriguing set of ribosomal proteins are those that bind directly and independently to the ribosomal RNAs and also autogeneously regulate ribosomal protein expression. In many cases the regulation is due to the protein recognition of the mRNA translational initiation region (2), although protein binding to a pre-mRNA splice site has also been observed (3). These instances of a single protein carrying out two different RNA-related functions provide interesting systems for studying how RNA recognition has evolved and is related to specific protein functions (4).In several instances there is convincing similarity between the secondary structures of the mRNA and rRNA targets of an autoregulatory ribosomal protein (4 -6). It is reasonable to conclude that both mRNA and rRNA bind in the same active site of any one of these proteins. In other cases there is no obvious similarity between the two RNA substrates. For instance, the mRNA target site for Escherichia coli S4 protein is a complex pseudoknot of about 110 nucleotides within the ␣ operon mRNA (7). Nearly the entire 5Ј domain of the 16 S rRNA, a fragment of 460 nucleotides, is needed to form the ribosomal binding site for the protein (8), although a smaller region is protected from cleavage by bound protein (9). There is no primary or secondary structural similarity between the two target sites, ...

The effects of soil temperature and other factors on the early spring growth of perennial ryegrass (Lolium perenne) swards were studied in 1983, 1984 and 1985. Leaf extension was used as the measure of growth and soil temperature was recorded at 10 cm depth below bare ground. Measurements were taken before the first nitrogen dressing had been applied each spring on swards that had received annual dressings of 0, 200 or 400 kg N ha‐1 since 1982. On the pooled data temperature alone accounted for 604% of the variation in leaf extension rate, with an average increase of 0·4 mm d‐1 for each 1°C increase in temperature over the range studied. Considering the data for each year separately did not greatly improve the correlation but did indicate that leaves extended more rapidly in 1985 for each degree increase in temperature whereas the smallest response was recorded in 1984. A better correlation was achieved by grouping data according to the nitrogen rates previously applied to plots and there was evidence of residual effets of this nitrogen. It seems likely that the differences between years can be explained in terms of differences in radiation and other environmental parameters over the measurement period, whereas the effects of previously applied nitrogen may be more closely related to physiological changes in the sward.

The effects of drainage on the yield of perennial ryegrass (Lolium perenne) swards grown for silage, and on soil development under grassland, were studied between 1982 and 1985.

The effect of temperature on the spring growth of perennial ryegrass swards was studied at three contrasting sites. Two of these were situated on land restored after opencast coal mining, one of which had been drained. The third was on undisturbed land of the same soil type. Rates of leaf extension were measured in an attempt to give an early indication of differences in plant growth in the spring of 1982.Spring growth started earliest on undisturbed land. On the restored land drainage proved beneficial, for although the onset of growth was delayed compared to the undisturbed site the subsequent rates of growth were similar. Both the onset and the rate of growth were slower on the undrained site. Highly significant relationships existed between leaf extension rate and soil temperature at each site. However, when sites were compared, differences in soil temperature could only partly explain observed differences in growth rate between sites.It was concluded that some factor other than soil temperature was responsible for the difference in spring growth between the undisturbed site and the undrained opencast site in this experiment.