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The hallmark feature of neurofibromatosis type 2 (NF2) is bilateral vestibular schwannomas. Vestibular schwannomas associated with NF2 have histologic features that make their resection more difficult, especially when preservation of hearing is a surgical goal. The presence of bilateral lesions complicates the treatment decision-making process. Because of their differences, vestibular schwannomas associated with NF2 merit consideration as a separate clinical entity from sporadic vestibular schwannomas. Understanding these differences and how they affect surgical and radiosurgical outcomes is important in understanding the disease process and related clinical management issues.

Surgical treatment of acoustic neuromas necessitates opening a corridor to the cerebellopontine angle and middle ear. Suboccipital and retrosigmoid craniotomies spare the petrous bone, and these approaches afford sufficient access for the safe and adequate resection of many tumors. These approaches may preserve hearing. Because of their size and extension into the middle ear, however, some acoustic neuromas require more extensive surgical exposure. In these cases, a petrosectomy can be performed. To minimize complications related to a complete petrosectomy, other approaches that remove variable amounts of the petrous bone have been developed. In contrast to suboccipital and retrosigmoid craniotomies, these approaches provide surgeons a wider working angle and more direct exposure of portions of tumor extending into the middle ear. Typically, these advantages are gained at the expense of hearing, however. This article reviews the surgical approaches that use a posterior petrosectomy to access acoustic neuromas: the retrolabyrinthine, translabyrinthine, and transcochlear approaches.

Acoustic neuromas often are located in the cerebellopontine angle. Their growth rate is estimated at 0.25 to 0.33 cm/yr. They become symptomatic with tinnitus, sensorineural hearing loss, and unsteadiness, and the mean latency from onset of symptoms to diagnosis is about 4 years. In the past, they tended to be detected when they were large enough to cause symptoms related to cerebellum or brain stem compression. Subtotal or complete resection of the lesion was usually mandatory to decompress the cerebellum and brain stem. With almost complete hearing loss occurring at this stage of tumor growth, hearing preservation was seldom a consideration. Magnetic resonance imaging now detects lesions as small as 1 mm, and many asymptomatic acoustic neuromas are identified incidentally. Patients may have no or few symptoms. Consequently, physicians need to have a comprehensive understanding of the histological and clinical behavior of acoustic neuromas and available screening tests to be able to choose among nonsurgical, radiosurgical, or surgical management options.

The RNA and protein products synthesized from ColE1 DNA were observed before and after cutting the DNA with different restriction enzymes. Synthesis was carried out in the DNA-directed coupled transcription translation system. The S-30 extracts used to catalyze synthesis were prepared from a recB mutant in which the linear DNA fragments resulting from restriction enzyme cleavage were spared from the usual degradation by exonucleolytic attack. By correlating the observed in vitro synthesized products with the location of the cleavage sites in the plasmid chromosome, it was possible to identify specific gene products. The col gene catalyzes the synthesis of numerous peptides in addition to the 56-kilodalton colicin protein encoded by this gene. Most of the subsidiary products appear to arise as the result of premature termination by a mechanism(s) which remains to be determined. A unique RNA and protein were characterized as products of the imm gene. The RNA has an estimated mass of 150 kilodaltons, and the protein has an estimated mass of 13 kilodaltons. From the DNA sequence of the chromosome, it was concluded that the transcripts from the imm and col genes must crisscross each other over a region of about 75 base pairs. Such a pattern of transcription might lead to interference of transcription of one gene by the other gene. Consistent with this hypothesis, it was found that imm gene transcription increased severalfold in vitro when the chromosome was cleaved in a way that eliminated transcription originating at the col gene promoter. Surprisingly, the increase in transcription by this mechanism did not result in a significant increase in the synthesis of the imm gene-encoded protein.

We have used the antibiotics coumermycin A1, novobiocin, and oxolinic acid, which are specific inhibitors of DNA gyrase, to study the coupled transcription and translation of several bacterial and plasmid genes in a DNA-directed cell-free system. The expression of different genes is reduced to different extents by inhibition of DNA gyrase activity. Among the genes tested, the lac operon, an rRNA gene, and the colicin gene of colicin E1 plasmid were found to be most sensitive, while the trp operon and some other genes in colicin E1 plasmid were relatively unaffected by the inhibitors. These results, together with earlier work on the transcription of circular DNA templates, indicate that DNA supercoiling can significantly enhance transcription from certain promoters.

A cell-free system derived from E. coli is described in which mature-sized 16S and 23S ribosomal RNAs (rRNA) are synthesized at a high relative rate, comprising 17-25% of the total transcription. The addition of guanosine tetraphosphate (ppGpp) to this system results in up to a 5-fold selective inhibition of rRNA accumulation. This effect is exerted at the level of synthesis rather than degradation. It is concluded that ppGpp, which is produced in large amounts by E. coli during amino-acid deprivation, could mediate the decrease in rRNA synthesis that accompanies such deprivation. The expression of other genes has also been investigated. No selective reduction of transfer RNA synthesis by ppGpp is observed. The trp and lac operons are found to be stimulated at the transcriptional level by the presence of this nucleotide. It is hypothesized that ppGpp interacts with the RNA polymerase in such a manner as to alter the affinity of the enzyme for promoters in an operon-specific fashion.

Synthesis of proteins encoded by the R222 plasmid was observed in a DNA-directed cell-free system and the products were compared to those plasmid proteins synthesized in Escherichia coli minicells. A greater number of plasmid-specified proteins was detected in the in vitro system than in the minicell, suggesting the presence of control factors for plasmid gene expression in the minicell. Synthesis of a newly detected plasmid protein (TET protein) is induced by tetracycline in minicells containing tetracycline-resistant plasmids, including R222, and this induced synthesis correlates with induced host resistance to the drug. This TET protein was synthesized in vitro from R222 DNA in the absence of tetracycline, indicating that no positive regulatory role for tetracycline is required for the protein's synthesis. TET proteon synthesis was inhibited in vitro when cell-free extracts prepared from cells containing the R222 plasmid were used.

After T4 bacteriophage infection of E. coli a complex series of events take place in the bacterium, including gross inhibition of host transcription and discrete changes in the classes of the genes of T4 that are transcribed. Accompanying these changes in the pattern of transcription one finds T4-induced changes in the RNA polymerase (EC 2.7.7.6; nucleosidetriphosphate:RNA nucleotidyltransferase). The effects of modified polymerase on transcription can be advantageously analyzed in a DNA-directed cell-free system for protein synthesis. In this system gene activity is measured indirectly by the amounts and types of proteins sythesized. In the DNA-directed cell-free system this modified polymerase, like normal polymerase, transcribes T4 DNA with a high efficiency but transcribes bacteriophage lambda and host DNA very poorly. Polymerase reconstruction experiments show that modification of the alpha subunit of the RNA polymerase is sufficient for inhibition of host transcription. Host transcription is also inhibited in vitro by T4 DNA. This latter type of inhibition is presumed to involve competition between host DNA and T4 DNA for some factor essential for transcription. The T4-modified polymerase transcribes from T4 DNA many of the same genes as normal unmodified polymerase; it also shows a capability for transcribing certain "non-early" T4 genes which is enhanced in the presence of protein-containing extracts from T4-infected cells.

Heretofore the DNA-directed coupled transcription-translation system, most useful in gene expression analysis, has been limited to the use of circular or long linear DNAs. Linear DNAs are degraded in this system by an exonucleolytic activity that can be eliminated by making the synthetic extracts from a suitable recB mutant of Escherichia coli. Using these extracts, we have examined the gene expression of a variety of linear DNAs. In particular, the complex pattern of expression of ribosomal protein genes and RNA polymerase genes in the rpoBC-rplLJ region has been analyzed by comparing the protein products obtained when using lambda rifd18 DNA with the product obtained when using the same DNA segmented with various restriction enzymes. The results obtained confirm the conclusions of others obtained by much more elaborate in vivo techniques. It seems highly likely that this cell-free system will have extensive applications in the area of analysis of gene expression.

cea, imm, and kil are a cluster of three functionally related genes of the plasmid ColE1. The cea and kil genes are in the same inducible operon, with transcription being initiated from a promoter adjacent to the cea gene. The imm gene is located between the cea and kil genes, but it is transcribed in the opposite direction. Complementary interaction between the imm mRNA and the anti-imm sequences in the middle of the cea-kil transcript causes a pronounced delay in expression of the kil gene when the cea-kil operon is induced. A segment in the overlapping region between the cea and imm genes causes delayed expression of the kil gene in the absence of imm gene transcription. This delay effect increases the yields of colicin synthesized in induced cells.

Escherichia coli cells containing the ColE1 plasmid or related plasmids are killed by considerably lower levels of mitomycin C (MTC) than are plasmid-free cells. Since exposure to MTC induces high levels of synthesis of the plasmid-encoded colicin toxin, it was originally thought that the killing effect was due to the increased levels of colicin. This possibility was discounted when it was shown that deletion mutations in the plasmid lacking most of the colicin (cea) gene still sensitized host cells to MTC. Only when the region containing the cea gene promoter was deleted did the killing effect disappear. This led to the suggestion that transcription originating from the cea gene promoter and not the colicin protein itself was required for killing. Transcription-blocking mutations in the cea gene support this suggestion. It was proposed that there is a gene (kil) located downstream from the cea gene in the same operon that is responsible for MTC killing and colicin transport. The precise location of the kil gene in ColE1 can be predicted by piecing together published sequence information. We used available sequence data to construct a number of well-defined plasmid mutants to further examine the relevance of transcription from the cea promoter and the kil gene to drug-induced killing and colicin transport. The most informative mutant had a small insertion in the kil gene. This mutant behaved as predicted; cells containing it had a greatly lowered sensitivity to MTC and were severely inhibited in the transport of colicin.

Colicin E1 is a small plasmid, containing the cea gene for colicin, the most prominent product of the plasmid. Colicin is a 56-kilodalton bacteriocin which is especially toxic to Escherichia coli cells that do not contain the plasmid. Under normal growth conditions very low levels of the plasmid are produced as a result of cea gene repression by the host LexA protein. Conditions that lower the concentration of LexA protein result in elevated levels of colicin synthesis. The LexA protein concentration can be lowered by exposing the cells to DNA-damaging reagents such as UV light or mitomycin C. This is because DNA damage signals the host SOS response; the response leads to activation of the RecA protease which degrades the LexA protein. DNA-damaging reagents result in very high levels of colicin synthesis and subsequent death of plasmid-bearing cells. Elevated levels of colicin are also produced in mutants of E. coli that are deficient in LexA protein. We found that comparably high levels of colicin can be produced in such mutants in the absence of cell death. In lexA strains carrying a defective LexA repressor, colicin synthesis shows a strong temperature dependence. Ten to twenty times more colicin is synthesized at 42 degrees C. This sharp dependence of synthesis on temperature suggests that there are factors other than the LexA protein which regulate colicin synthesis.

The deoxyribonucleic acid (DNA) from Escherichia coli has been isolated as an extract containing about 50 per cent by weight protein. The protein component differs both in composition and chemical behaviour from histone which occurs in combination with the DNA in most cells of higher organisms. Although this result suggests the absence of histone-like protein, it is not clear whether the bacterial protein found is naturally bound to the bacterial DNA in the cell or becomes attached to the DNA during the course of isolation.

X-ray diffraction photographs of a nucleoprotein preparation from Escherichia coli show the A-type pattern of crystalline deoxyribonucleic acid (DNA). This suggests that a large part of the DNA is free from protein. In higher organisms DNA does not exist in this form but is closely bound to protein.

An assay system for the in vitrotranscription of the lacoperon is described. A protein factor (CAP) and cyclic AMP, which are essential for the lacexpression in vivo, also stimulate lactranscription in vitro.