The yeast PRP28 g ene has been implicated in nuclear precursor messenger RNA (pre-mRNA) splicing, a two-step reaction involved in a multitude of RNA structural alterations. Prp28p, the gene product of PRP28 , is a member of the evolutionarily conserved DEAD-box proteins (DBPs). Members of DBPs are involved in a variety of RNA-related biochemical processes, presumably by their putative RNA helicase activities. Prp28p has been speculated to play a role in melting the duplex between U4 and U6 small nuclear RNAs (snRNAs), leading to the formation of an active spliceosome. To study the function of Prp28p and its interactions with other components of the splicing machinery, we have isolated and characterized a large number of prp28 conditional mutants. Strikingly, many of these prp28 mutations are localized in the highly conserved motifs found in all the DBPs. Intragenic reversion analysis suggests that regions of motifs II, III and V, as well as of motifs I and IV, in Prp28p are likely to be in close proximity to each other. Our results thus provide the first hint of the local structural arrangement for Prp28p, and perhaps for other DBPs as well.

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One-third octave band and narrowband llpectra and continuous directivity patterns radiated from an inlet are presented over ranses of fan operating conditions, tunnel velocity, and anale of attack.. Tunnel flow markedly reduced the unsteadiness and level of the blade passa .. tone, revealed the cutoff design faature of tne blade passa .. tone, and exposed a lobular directivity pattern for the second haraDnic tone. The full effects of tunnel flow are shown to be complete above a tunnel velocity of 2r mKters/second. The acoustic signatures are also shown to be strongly affected by fan rotational speed, fan blade loading, and inlet angle of sttack.The inability of ground-static acoustic tests to yield turbofan engine fan acoustic characteristics indicative of thst which would be messured during flignt is well documented. Refs. 1 through 7 all indicate that inflow disturbances present during static tests and absent under flignt conditions interact with the rotor to generate tone and broadband noise not present during flight. This noise resulting from the rotor interacting with inflow disturbances tends to mask the benefits attained through design techniques aimed st redUCing rotor/atator interaction noise levels. Refs. 8 through 14 attest to the number of investigations that have attempted to eliminste the excess noise in ground based facilities. These attempts have realized varying degrees of succeas.An approach to Simulating flight conditions is through the use of an anechoic wind tunnel. To this end the NASA-Lewis 9 by 15 low speed wind tunnel has been modified to achieve near anechoic or free-field properties in the test section. The capabtlities and limitationa of the facility are descriDed in Refs. 1,15, and 16. Ref. 1, in particular, concludea that the anechoic wind tunnel is a useful facility for applied research on aircraft engine fan noise during flight.The purpose of this paper ia to prupnt representative model fan noise data indicating the type of acoustic information that can be obtained in the NASA-Lewis anechoic wind tunnel. The model fan used for the test is designed to have the blade passage tone iUI-off below 107% of the design rotational speed. , 7,18,19 Where applicable, the results of the teat are related to known forward flight effects and to the rotor/stator cut-off theory . 17 One-third octave band and narrowband spectra .. well as continuous directivity patterns radiated from an inlet are presented. Data are shown over a range of conditions. The fan operating conditions varied include the rotational speed from 79 to 116% of the design value and the nozzle exit araa. The ranges of wind tunnel airflow velocities and inlet angle of attack are zero to 43 m/sec and zero to 30~ respectively. ApparatusAnechoic Wind Tunnel Fig. 1 ia a schematic representation of the NASA-Lewis 8-by 6-foot 20 and 9-by l5-foot wind tunnels. 21 The NASA-Lewis anechoic wind tunnel is the terminology used to refer to the combination of the 9-by l5-foot low speed test section, the tunnel drive motors, and enclos...

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